Welcome to Infoguyz

How Streaming Video and Audio Work

2010-05-10T07:32:00.000-07:00

In the early days of streaming media -- the mid-to-late 1990s --
watching videos and listening to music online wasn't always fun. It was a little like driving in stop-and-go traffic during a heavy rain. If you had a slow computer or a dial-up Internet connection, you could spend more time staring at the word "buffering" on a status bar than watching videos or listening to songs. On top of that,everything was choppy, pixilated and hard to see.

Streaming video and audio have come a long way since then. According to Bridge Ratings, 57 million people listen to Internet radio every week. In 2006, people watched more than a million streaming videos a day on YouTube . The same year, television network ABC started streaming its most popular TV shows over the Web. People who missed an episode of shows like "Lost" or "Grey's Anatomy" could catch up on the entire thing online -- legally and for free.

Streaming videos directly to computer

The success of streaming media is pretty recent, but the idea behind it has been around as long as people have. When someone talks to you, information travels toward you in the form of a sound wave. Your ears and brain decode this information, allowing you to understand it. This is also what happens when you watch TV or listen to the radio. Information travels to an electronic device in the form of a cable signal, a satellite signal or radio waves. The device decodes and displays the signal.

In streaming video and audio, the traveling information is a stream of data from a server. The decoder is a stand-alone player or a plugin that works as part of a Web browser. The server, information stream and decoder work together to let people watch live or prerecorded broadcasts.

The basic preview of streaming video [windows 7 first look review]

Click here for "Finding and Playing Streaming Video and Audio"

How Touch pad works ?

2009-11-22T18:04:00.000-08:00

A touchpad (also trackpad) is a pointing device consisting of specialized surface that can translate the motion and position of a user's fingers to a relative position on screen. They are a common feature of laptop computers and also used as a substitute for a computer mouse where desk space is scarce. Touchpads vary in size but are rarely made larger than 40 square centimeters (about 6 square inches). They can also be found on personal digital assistants (PDAs) and some portable media players, such as the Zune using the Zune Pad.

working and operation click here >>

Optimus keyboard

2009-09-19T18:49:00.000-07:00

The Optimus Maximus keyboard, previously just "Optimus keyboard", is a keyboard developed by the Art. Lebedev Studio, a Russian design studio headed by Artemy Lebedev. Each of its keys is a display which can dynamically change to adapt to the keyboard layout in use or to show the function of the key. Pre-orders began on 20 May 2007 for a limited production run from December 2007 to January 2008, with a second batch expected to arrive in February 2008. It first started shipping the week of February 21, 2008.

Overview

The design featured on the studio's website received attention on the web when it was featured on Slashdot on 14 July 2005, and afterwards for a few weeks on other technology websites. The original release date was "end of 2006", however production issues caused the Optimus mini three to be developed first, with the full keyboard delayed until the end of 2007. The keyboard was number 10 in the Wired Magazine 2006 Vaporware Awards and number 4 on the list in 2007 due to its numerous delays and feature reductions.

The Optimus allows for greater user interaction, by dynamically displaying the current function of the keys. For example, when the user presses the shift key, the pictures would change to upper-case versions. It would also make switching between different keyboard layouts (such as English and Cyrillic) rapid, and could make the switch to alternative layouts such as Dvorak easier for people who only have a QWERTY keyboard with no possibility of rearranging the keys. To demonstrate this concept, there are computer renderings showing example layouts for Quake III Arena and Adobe Photoshop.

A newly-revealed (as of January 3, 2008) patent application filed on March 13, 2007 suggests that Apple Inc. may be working on a similar dynamically changeable OLED keyboard

Optimus mini three

Art. Lebedev Studio has released a smaller three-key version of their keyboard, named Optimus mini three. Each of the keys is larger than a standard key. The mini three can be adjusted, through the configuration software, to either a horizontal or vertical orientation.

Initial reviews have been mixed. The keyboard functions as advertised, but it has been criticized for inordinately high CPU usage, slow response time, and buggy configuration software

Optimus Aux

On July 21, 2008, Engadget posted about a new version of the keyboard, named Optimus Pultius. It features 15 OLED keys in a three-by-five arrangement and a USB port. It is expected to be released in late 2008 or early 2009.[6][7] On September 19, 2008, Engadget also reported that the Pultius had been renamed to the Aux[8] and included a new rendering of the rear side showing that there would be two USB ports instead of one.

Variations

Variations with fewer OLED keys will also be available, each upgradeable by replacing static keys with OLED keys after purchase. For keyboards with less than a full complement of OLED "active keys", additional keys can be purchased and installed.

Special Features

Art. Lebedev Studio is expecting to manufacture the keyboard with these features:[3]

* A plastic body (width: 537 mm, depth: 173 mm, height: 38 mm)
* Extra-durable polymer plastic keys (20.2×20.2 mm, visible area 10.1×10.1 mm)
* 48×48 pixel screens, Highcolor mode (65 536 colors, 10 FPS)
* OLED (Organic Light Emitting Diode) screen for keys
* USB 2.0 (or 1.1) connectivity
* 4-5 year lifetime
* A key-saver mode
* Support for animation on keys at 10 FPS minimum
* Ability to form a mosaic using a combination of key images
* Compatibility with Windows XP, Windows Vista and Mac OS X 10.5.1 (and higher).
* An SDK for complete display customization
* Swappable keys and support for keys without displays
* 32 MB SD card for storing basic layouts
* Non-stop glow time at nominal brightness of 20,000 hours, after which display quality will diminish
* An ambient light sensor which can be used to automatically adjust display brightness
* A viewing angle of 160°

More images and videos of "Optimus keyboard" >>>

What is phishing?

2009-09-09T16:21:00.000-07:00

INTRODUCTION:

In the field of computer security, phishing is the criminally fraudulent process of attempting to acquire sensitive information such as usernames, passwords and credit card details by masquerading as a trustworthy entity in an electronic communication.

Phishing is a scam in which the attacker sends an email purporting to be from a valid financial or eCommerce provider. The email often uses fear tactics in an effort to entice the intended victim into visiting a fraudulent website. Once on the website, which generally looks and feels much like the valid eCommerce/banking site, the victim is instructed to login to their account and enter sensitive financial information such as their bank PIN number, their Social Security number, mother's maiden name, etc. This information is then surreptitiously sent to the attacker who then uses it to engage in credit card and bank fraud - or outright identity theft.

Many of these phishing email appear to be quite legitimate. Don't be a victim. Look over the following examples of phishing scams to familiarize yourself with the clever techniques used.

Click here to see the examples

How Photocopiers Work ..??

2009-08-08T08:13:00.000-07:00

How Photocopiers Work

A typical business photocopier from Xerox

Walk into almost any business office, and you'll probably find a photocopier ("copier") with a line of people waiting to use it. For most businesses, small or large, the copier has become standard equipment, much like having a desk to work at and a chair to sit in.

What if you had to resort to making carbon copies of important documents, as many people did before copiers came along? Or worse, imagine how tedious it would be if you had to recopy everything by hand! Most of us don't think about what's going on inside a copier while we wait for copies to shoot neatly out into the paper tray, but it's pretty amazing to think that, in mere seconds, you can produce an exact replica of what's on a sheet of paper! In this article, we will explore what happens after you press "Start" on a photocopier.

A typical business photocopier from Xerox

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What is Web hosting..?

2009-07-31T23:55:00.000-07:00

A web hosting service is a type of Internet hosting service that allows individuals and organizations to provide their own website accessible via the World Wide Web. Web hosts are companies that provide space on a server they own or lease for use by their clients as well as providing Internet connectivity, typically in a data center. Web hosts can also provide data center space and connectivity to the Internet for servers they do not own to be located in their data center, called colocation.

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Operating System (starring Linux)

2009-07-28T08:03:00.000-07:00

Introduction:

Every desktop computer uses an operating system. The most popular operating systems in use today are:

Windows
Mac OS
UNIX

Linux is an operating system -- very much like UNIX -- that has become very popular over the last several years.

CLICK HERE TO READ MORE>>>

Get Familiar with these extensions .....

2009-07-20T17:54:00.000-07:00

Sound :

MPEG-1/2 Audio Layer 3 (.mp3)
Ogg Vorbis (.ogg)
ASF Audio (.asf,.wma)
Wave form audio format (.wav)
RealAudio (.ra,.rm)
Free Lossless Audio codec(.flac)
Advanced Audio coding (.aac)
MPEG-4 advanced audio coding (.m4a,.mp4)
Musepack (.mpc)
TwinVQ(.vqf)
3GP Music (.3gp)
AC3 Audio File (.ac3)
Adaptive Multi-Rate (.amr)
Adaptive Multi-Rate WB (.awb)
Sun Mircrosystem's audio format (.au,.snd)
Audio Interchange File Format (.aiff)
Purevoice File (.qcp)
AMIGA 8bit sound file (.8svx)
PSION sound file (.prc)
IRCAM sound file (.sf)
soundTool (.sndt)
PSION 8bit sound file (.wve)
soundtracker module (.mod)
FastTracker II module (.xm)
ImpulseTracker module (.it)
ScreamTracker module (.s3m)

Ringtone (Monophonic/Polyphonic) :

MIDI-0 (.mid,.midi)
SP-MIDI (.mid,.midi)
Midi Karaoke (.kar)
MMF/SMAF-1 (.mmf,.smaf)
Qualcomm CMX 3.0 (.pmd)
Motorola Ringtone (.mot)
Sagem Ringtone (.sagem)
Sagem Ringtone (.sagem21)
Ericsson emelody (.emy)
iMelody Ringtone Format (.imv)
Ringtones text transfer language (.rttl,.rtx)
Nokia phone Ring Tone (.nokia,.ott)
Nokia Phone Ring Tone (.noktxt)

Image :

Joint photographic experts group (.jfif,.jif,.jpe,.jpeg,.jpg)
Windows bitmap (.bmp)
Graphics interchange format (.gif)
Truevision TGA (.tga)
Portable network graphics (.pgm)
AVS X image (.avs)
Kodak Cineon Image Format (.cin)
ZSoft IBM PC multi-page paintbrush (.dcx)
Windows device independent bitmap (.dib)
SMPTE digital moving picture exchange (.dpx)
Microsoft icon (.ico)
Magick image file format (.miff)
On-the-air-Bitmap (.otb)
Palm pixmap (.palm)
Portable bitmap format black/white (.pbm)
Xv's Visual Schnauzer thumbnail (.p7)
Photo CD (.pcd)
Zsoft IBM PC Paintbrush file (.pcx)
Apple Mcintosh QuickDraw (.pict)
Portable Pixmap format - color (.ppm)
Adobe Photoshop bitmap file (.psd)
Photo CD - sRGB color (.pcds)
Irix RGB image (.sgi)
SUN Raster Image (.ras,.sun)
X Windows system bitmap black/white (.xbm)
X Windows system pixmap (.xpm)
CCIR 601 4:1:1 (.yuv)

Vector Document :

Windows Metafile (.wmf)
Scalable Vector Graphics (.svg)
Magick Vector Graphics (.mvg)
AutoCAD Interchange Format (.dxf)
Enhanced Metafile (.emf)
Encapsulated Postscript (.eps)
Computer Graphics Metafile (.cgm)
OS/w Metafile (.met)
OpenOffice 2.0 Draw Document (.odg)
OpenOffice 2.0 Draw Template (.otg)
OpenOffice 1.0 Draw Document (.sxd)
OpenOffice 1.0 Draw Template (.std)

Document :

Text files (.txt)
Url address (web) (.url)
HyperTextMarkup Language (.htm,.html)
XHTML (.xhtml)
Rich Text Format/MS Word (.rtf)
Portable Document Format (.pdf)
Adobe Postscript (.ps)
Microsoft Word (.doc)
MS Word template (.dot)
OpenOffice 2.0 Text Document (.odt)
OpenOffice 2.0 Text Template (.ott)
OpenOffice 1.0 Text Document (.sxw)
OpenOffice 1.0 Text Template (.stw)
AportisDoc Palm DB (.pdb)
Starwriter vorlage/Template (.vor)
PocketWord (.psw)
Wordperfect 6 (.wpd)
MS Word 2003 XML (.xml)

Data :

Data Interchange Format (.dif)
dBASE (.dbf)
Microsoft Excel (.xls)
MS Excel Vorlage/Template (.xlt)
Pocket Excel (.pxl)
SYLK (.slk)
Lotus 1-2-3 (.123,.wk1)
StarCalc (.sdc)
StarCalc Template (.vor)
OpenOffice 2.0 Spreadsheet (.ods)
OpenOffice 2.0 Calc template (.ots)
OpenOffice 1.0 spreadsheet (.sxc)
OpenOffice 1.0 calc template (.stc)

Mathematics :

MathML (.mml)
StarMath (.smf)
OpenOffice 2.0 Math (.odf)
OpenOffice 1.0 Math (.sxm)

Presentation :

Microsoft Powerpoint (.ppt)
Microsoft Powerpoint Template (.pot)
StarImpress 5.0 (.sdd)
StarImpress 5.0 Template (.vor)
StarImpress 4.0 (.sdd)
StarImpress 4.0 Template (.vor)
OpenOffice 2.0 Impress (.odp)
OpenOffice 2.0 Impress Template (.otp)
OpenOffice 1.0 Impress (.sxi)
OpenOffice 1.0 Impress Template (.sti)

Compressed archives:

Data compression (.zip)
7Z Archive (.7z)
LHA Archive (.lha,.lzh)
Roshal ArchiveArchive (.rar)
Tape ARchive (.tar)
TAR Gzip Compressed archive (.gz)
BZ2 compressed archive (.bza)
Deepfreezer YZ1 archive (.yz1)

Movie:

Windows Media Video (.wmv)
3GP/3G2 Video (.3gp)
Audio Video Interleave (.avi)
Matroska (.mkv)
Apple Quicktime (.mov)
Motion Picture Expert Group (.pg)
Ogg vorbis Compressed video (.ogm)
MPEG-4 (.mp4)
Flash Video (.flv)
DVD Video Object (.vob)
FLIC Animation (.fli)
Digital Video (.dv)
ASF Video (.asf)
Google Video File (.gvi)

Browse your friend computer from ur home

2009-07-16T08:12:00.000-07:00

Hello guyz .. this is the software which u can browse your friends computer through your PC and even u can do every thing. Its very easy and useful for us to help our friends with their computer problems.This software allows you to access your friend's computer and then solve the problem by sitting at your home no matter if u r on other OTHER end of the world. Just go to this link download and install that software and have fun...

click here for link

and even your friend should install it .......

click here "How to install"

Free Vista ShutdownTimer

2009-07-11T09:43:00.000-07:00

Vista Shutdown timer is a free software...

Screen shot:

MORE SCREEN SHOTS

click here to Download Vista-Shutdown Timer 1.6.5

Info on speech recognition

2009-07-10T06:07:00.000-07:00

INTRODUCTION:

Today, when we call most large companies, a person doesn't usually answer the phone. Instead, an automated voice recording answers and instructs you to press buttons to move through option menus. Many companies have moved beyond requiring you to press buttons, though. Often you can just speak certain words (again, as instructed by a recording) to get what you need. The system that makes this possible is a type of speech recognition program -- an automated phone system.

You an also use speech recognition software in homes and businesses. A range of software products allows users to dictate to their computer and have their words converted to text in a word processing or e-mail document. You can access function commands, such as opening files and accessing menus, with voice instructions. Some programs are for specific business settings, such as medical or legal transcription.

People with disabilities that prevent them from typing have also adopted speech-recognition systems. If a user has lost the use of his hands, or for visually impaired users when it is not possible or convenient to use a Braille keyboard, the systems allow personal expression through dictation as well as control of many computer tasks. Some programs save users' speech data after every session, allowing people with progressive speech deterioriation to continue to dictate to their computers.

For more info click here

Working Of CRT..

2009-06-26T00:30:00.000-07:00

CRT Monitors

A CRT [Cathode Ray Tube]monitor contains millions of tiny red, green, and blue phosphor dots that glow when struck by an electron beam that travels across the screen to create a visible image. The illustration below shows how this works inside a CRT.

The terms anode and cathode are used in electronics as synonyms for positive and negative terminals. For example, you could refer to the positive terminal of a battery as the anode and the negative terminal as the cathode.

In a cathode ray tube, the "cathode" is a heated filament. The heated filament is in a vacuum created inside a glass "tube." The "ray" is a stream of electrons generated by an electron gun that naturally pour off a heated cathode into the vacuum. Electrons are negative. The anode is positive, so it attracts the electrons pouring off the cathode. This screen is coated with phosphor, an organic material that glows when struck by the electron beam.

There are three ways to filter the electron beam in order to obtain the correct image on the monitor screen: shadow mask, aperture grill and slot mask. These technologies also impact the sharpness of the monitor's display. Let's take a closer look at these now.

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INTEL 8085 Microprocessor

2009-06-24T08:45:00.000-07:00

INTEL 8085:

The Intel 8085 is an 8-bit microprocessor introduced by Intel in 1977. It was binary-compatible with the more-famous Intel 8080 but required less supporting hardware, thus allowing simpler and less expensive microcomputer systems to be built.

The "5" in the model number came from the fact that the 8085 required only a +5-volt (V) power supply rather than the +5V, -5V and +12V supplies the 8080 needed. Both processors were sometimes used in computers running the CP/M operating system, and the 8085 later saw use as a microcontroller (much by virtue of its component count reducing feature). Both designs were eclipsed for desktop computers by the compatible but more capable Zilog Z80, which took over most of the CP/M computer market as well as taking a large share of the booming home computer market in the early-to-mid-1980s.

INTEL 8085 Mp

The 8085 had a very long life as a controller. Once designed into such products as the DECtape controller and the VT100 video terminal in the late 1970s, it continued to serve for new production throughout the life span of those products (generally many times longer than the new manufacture lifespan of desktop computers).

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What is a Microprocessor ? [Deep Explanation]

2009-06-24T07:40:00.000-07:00

Intel 4004 first Microprocessor

A microprocessor incorporates most or all of the functions of a central processing unit (CPU) on a single integrated circuit (IC). The first microprocessors emerged in the early 1970s and were used for electronic calculators, using binary-coded decimal (BCD) arithmetic on 4-bit words. Other embedded uses of 4- and 8-bit microprocessors, such as terminals, printers, various kinds of automation etc, followed rather quickly. Affordable 8-bit microprocessors with 16-bit addressing also led to the first general purpose microcomputers in the mid-1970s. The recent development of fast microprocessors is also linked to the growing popularity of fourth generation programming languages.

Computer processors were for a long period constructed out of small and medium-scale ICs containing the equivalent of a few to a few hundred transistors. The integration of the whole CPU onto a single VLSI chip therefore greatly reduced the cost of processing capacity. From their humble beginnings, continued increases in microprocessor capacity have rendered other forms of computers almost completely obsolete ( history of computing hardware), with one or more microprocessor as processing element in everything from the smallest embedded systems and handheld devices to the largest mainframes and supercomputers.

Since the early 1970s, the increase in capacity of microprocessors has been known to generally follow Moore's Law, which suggests that the complexity of an integrated circuit, with respect to minimum component cost, doubles every two years. In the late 1990s, and in the high-performance microprocessor segment, heat generation (TDP), due to switching losses, static current leakage, and other factors, emerged as a leading

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515 Tutorials in one pack. U Never Wanna Miss That

2009-06-20T05:36:00.000-07:00

Here is the 515 tutorials of my collection i think this may help you ...all material is in text format only....

Click here for the list of Tutorials

How to solve basic Dual Boot Issues

2009-06-19T07:55:00.000-07:00

These are the collection for having Dual Booting problems...I think this may solve that

Case 1:
You have Dual Boot Win7 and XP/Vista and you lost the XP/Vista boot option at startup, but Win7 boots fine.

Solution:
1.) Start Win7.

2.) If you can see your XP/Vista partition in Computer, write down the drive letter (e.g. D)

3.) If you can't see the XP partition and you see all others but this one, open Control Panel - Administrative Tools - Computer Management -> Disk Management(left pane) and right-click the partition without a drive letter, choose "Change drive letters and paths" and assign a drive letter for the partition, e.g. D:

4.) Open an elevated command prompt and type the following lines followed by Enter for each line, changing the drive letter D: (in blue) with the one on your XP/Vista partition:

FOR RESTORING XP:

bcdedit /create {ntldr} /d "Windows XP"

bcdedit /set {ntldr} device partition=D:

bcdedit /set {ntldr} path \ntldr

bcdedit /displayorder {ntldr} /addlast

FOR RESTORING VISTA:

bcdedit /copy {current} /d "Windows Vista"

(You will get a response saying that a new {UUID} was created successfully. Write down or copy the new UUID.)

bcdedit /set {place_new_UUID_here} device partition=D:
bcdedit /set {place_new_UUID_here} osdevice partition=D:

5.) Done

Case 2:
You have Dual Boot Win7 and XP/Vista and you lost the Win7 boot option at startup, but XP/Vista boots fine.

Solution:

1. Insert the Win7 Installation DVD and boot your computer with it (as if you were making an installation).

2. At the first screen , select your language etc and press enter.

3. At the second screen, click "Repair Computer" at the bottom left.

4. Wait until startup repair is finished and reboot.

5. Done. You can now boot Win7.

Case 3: You have restored booting Win7 using the Case 2 method or other way, but now you've lost XP/VISTA .

Solution: Follow Case 1 Solution.

Case 4: You want Win7/Mac Dual Boot.

Solution: Follow these instructions: OSX and Windows 7 Dual Boot Hope it helps

Download this via E book

Overclocking

2009-06-15T18:13:00.000-07:00

Info on overclocking:

Introduction:

Many people probably don't know what overclocking is but have possibly heard the term used before. To put it in its simplest terms, overclocking is taking a computer component such as a processor and running at a specification higher than rated by the manufacturer. Every part produced by companies such as Intel and AMD are rated for a specific speeds. They have tested the capabilities of the part and certified it for that given speed. Of course, most parts are underrated for increased reliability. Overclocking a part simply takes advantage of the remaining potential out of a computer part that the manufacturer is unwilling to certify the part for but it is capable of.

click here to read more

Info on top 10 viruses in this world

2009-06-15T04:32:00.000-07:00

Introduction:

Computer viruses can be a nightmare. Some can wipe out the information on a hard drive, tie up traffic on a computer network for hours, turn an innocent machine into a zombie and replicate and send themselves to other computers. If you've never had a machine fall victim to a computer virus, you may wonder what the fuss is about. But the concern is understandable

-- according to Consumer Reports, computer viruses helped contribute to $8.5 billion in consumer losses in 2008. Computer viruses are just one kind of online threat, but they're arguably the best known of the bunch.

Click Here to see Description on Top 10 Viruses

Video tutorials for Java

2009-06-09T08:38:00.000-07:00

Video tutorials from VTC.com

Click Here for More Details and Downloads

Easy Torrent Explained

2009-06-09T08:30:00.000-07:00

Torrents Explained...

Torrent is a very small file whose file name ends with " .torrent " extension. It (A torrent file) contains all the information about the file to be downloaded like file name, file size, date of creation and some other information. A torrent file also contains a list of trackers. You can download very large files like games, movies, videos etc very easily using torrents. You can also use torrents to share files with your friends instead of sharing files through messengers.

What is a tracker ?
A tracker is a computer on the internet. It comes into action as soon as you open the .torrent file using a torrent client. Tracker manages the torrent file on the internet. Tracker also allows the parts of the file to be downloaded from more than one server.

What is a seeder ?
A seeder is a person who has more than 0% of the file associated with the torrent file.

What is a leecher ?
A leecher is a person who is attempting to download the files through torrent.

The downloading time will depend on the number of seeders and leechers. More the seeders, lesser the time and more the leechers, more the time.

How to download files using torrent ?

It is very easy to download through torrents. First of all download and install a torrent client software. You need this software to open torrent files. uTorrent is one of the best torrent client software. Now find a file that you want to download from a torrent search engine.

After you find the desired file, the torrent search engine will allow you to download a .torrent file. Download that torrent file. Now open this torrent file using uTorrent (Or any other client software) and it will start download the file for you.

CCNA Tutorial in simple PowerPoint Presentations [New]

2009-06-09T07:58:00.000-07:00

CCNA Tutorial in just 5.5MB with Power Point presentation download and enjoy

Click Here to Download

How To Install Windows Server 2008

2009-06-08T08:50:00.000-07:00

Server 2008 E-book Explained by step by step process hope you liked this description

here's the download link from Mediafire server only

[500 Kilobytes file size ] [ .pdf Format]

http://www.mediafire.com/download.php?jztz3ng0tmm

CCNA Exam Prep (Exam 640-802)

2009-06-08T07:59:00.001-07:00

Book Description :::::::::

The CCNA Exam Prep, Second Edition, is an in-depth training guide for the new CCNA (Cisco Certified Network Associate) certification from Cisco. Published in the popular Exam Prep series, the book incorporates all the topics tested in this newly-revised exam, including new security, VPN, wireless, IPv6, and troubleshooting coverage. The authors emphasize sub-netting concepts because this is historically a difficult roadblock for Cisco certification candidates. This Exam Prep covers all the exam objectives and will give you a thorough understanding of each testable concept in addition to real-world configuration examples for configuring a wide range of Cisco devices. The Prep begins with an objectives quick reference and includes chapter summaries with a list of key terms, exercises, review questions, and an exam on chapter content with detailed answers. Exam Preps include notes, tips, cautions, and exam alerts to help you focus on important issues. If you are preparing for this exam you will find the Exam Prep series to be the complete certification solution for the CCNA exam.

# 1008 pages
# Publisher: Que; 2 edition (December 28, 2007)
# Language: English
# ISBN-10: 0789737132
# ISBN-13: 978-0789737137

http://rapidshare.com/files/85404805/02.2tion.De32.pdf

HowStuffWorks-Flash collection-365 flash files

2009-06-08T07:34:00.000-07:00

Click Here to Download

How Speakers Work??

2009-05-26T07:35:00.000-07:00

In any sound system, ultimate quality depends on the speakers. The best recording, encoded on the most advanced storage device and played by a top-of-the-line deck and amplifier, will sound awful if the system is hooked up to poor speakers.

A system's speaker is the component that takes the electronic signal stored on things like CDs, tapes and DVDs and turns it back into actual sound that we can hear.

In this article, we'll find out exactly how speakers do this. We'll also look at how speaker designs differ, and see how these differences affect sound quality. Speakers are amazing pieces of technology that have had a profound impact on our culture. But at their heart, they are remarkably simple devices.

Sound Basics

To understand how speakers work, you first need to understand how sound works.

Inside your ear is a very thin piece of skin called the eardrum. When your eardrum vibrates, your brain interprets the vibrations as sound -- that's how you hear. Rapid changes in air pressure are the most common thing to vibrate your eardrum.

An object produces sound when it vibrates in air (sound can also travel through liquids and solids, but air is the transmission medium when we listen to speakers). When something vibrates, it moves the air particles around it. Those air particles in turn move the air particles around them, carrying the pulse of the vibration through the air as a traveling disturbance.

To see how this works, let's look at a simple vibrating object -- a bell. When you ring a bell, the metal vibrates -- flexes in and out -- rapidly. When it flexes out on one side, it pushes out on the surrounding air particles on that side. These air particles then collide with the particles in front of them, which collide with the particles in front of them and so on. When the bell flexes away, it pulls in on these surrounding air particles, creating a drop in pressure that pulls in on more surrounding air particles, which creates another drop in pressure that pulls in particles that are even farther out and so on. This decreasing of pressure is called rarefaction.

In this way, a vibrating object sends a wave of pressure fluctuation through the atmosphere. When the fluctuation wave reaches your ear, it vibrates the eardrum back and forth. Our brain interprets this motion as sound.

Differentiating Sound

We hear different sounds from different vibrating objects because of variations in:

* Sound-wave frequency - A higher wave frequency simply means that the air pressure fluctuates faster. We hear this as a higher pitch. When there are fewer fluctuations in a period of time, the pitch is lower.

* Air-pressure level - This is the wave's amplitude, which determines how loud the sound is. Sound waves with greater amplitudes move our ear drums more, and we register this sensation as a higher volume.

A microphone works something like our ears. It has a diaphragm that is vibrated by sound waves in an area. The signal from a microphone gets encoded on a tape or CD as an electrical signal. When you play this signal back on your stereo, the amplifier sends it to the speaker, which re-interprets it into physical vibrations. Good speakers are optimized to produce extremely accurate fluctuations in air pressure, just like the ones originally picked up by the microphone. In the next section, we'll see how the speaker accomplishes this.

Making Sound

In the last section, we saw that sound travels in waves of air pressure fluctuation, and that we hear sounds differently depending on the frequency and amplitude of these waves. We also learned that microphones translate sound waves into electrical signals, which can be encoded onto CDs, tapes, LPs, etc. Players convert this stored information back into an electric current for use in the stereo system.

Making Sound: Diaphragm

A driver produces sound waves by rapidly vibrating a flexible cone, or diaphragm.

* The cone, usually made of paper, plastic or metal, is attached on the wide end to the suspension.
* The suspension, or surround, is a rim of flexible material that allows the cone to move, and is attached to the driver's metal frame, called the basket.
* The narrow end of the cone is connected to the voice coil.
* The coil is attached to the basket by the spider, a ring of flexible material. The spider holds the coil in position, but allows it to move freely back and forth.

Some drivers have a dome instead of a cone. A dome is just a diaphragm that extends out instead of tapering in.

A speaker is essentially the final translation machine -- the reverse of the microphone. It takes the electrical signal and translates it back into physical vibrations to create sound waves. When everything is working as it should, the speaker produces nearly the same vibrations that the microphone originally recorded and encoded on a tape, CD, LP, etc.

A typical speaker driver, with a metal basket, heavy permanent magnet and paper diaphragm

Making Sound: Voice Coil

The voice coil is a basic electromagnet.

If you've read How Electromagnets Work, then you know that an electromagnet is a coil of wire, usually wrapped around a piece of magnetic metal, such as iron. Running electrical current through the wire creates a magnetic field around the coil, magnetizing the metal it is wrapped around. The field acts just like the magnetic field around a permanent magnet: It has a polar orientation -- a "north" end and and a "south" end -- and it is attracted to iron objects. But unlike a permanent magnet, in an electromagnet you can alter the orientation of the poles. If you reverse the flow of the current, the north and south ends of the electromagnet switch.

This is exactly what a stereo signal does -- it constantly reverses the flow of electricity. If you've ever hooked up a stereo system, then you know that there are two output wires for each speaker -- typically a black one and a red one

The wire that runs through the speaker system connects to two hook-up jacks on the driver.

Essentially, the amplifier is constantly switching the electrical signal, fluctuating between a positive charge and a negative charge on the red wire. Since electrons always flow in the same direction between positively charged particles and negatively charged particles, the current going through the speaker moves one way and then reverses and flows the other way. This alternating current causes the polar orientation of the electromagnet to reverse itself many times a second.

Driver Types

In the last section, we saw that traditional speakers produce sound by pushing and pulling an electromagnet attached to a flexible cone. Although drivers are all based on the same concept, there is a wide range in driver size and power. The basic driver types are:

* Woofers
* Tweeters
* Midrange

WOOFER

Tweeters

midrange

Woofers are the biggest drivers, and are designed to produce low frequency sounds. Tweeters are much smaller units, designed to produce the highest frequencies. Midrange speakers produce a range of frequencies in the middle of the sound spectrum.

And if you think about it, this makes perfect sense. To create higher frequency waves -- waves in which the points of high pressure and low pressure are closer together -- the driver diaphragm must vibrate more quickly. This is harder to do with a large cone because of the mass of the cone. Conversely, it's harder to get a small driver to vibrate slowly enough to produce very low frequency sounds. It's more suited to rapid movement.

Know about Microsoft....

2009-05-02T07:37:00.000-07:00

The sign at a main entrance to the Microsoft corporate campus. The Redmond Microsoft campus today includes more than 8 million square feet (approx. 750,000 m²) and over 30,000 employees.

Microsoft Corporation (NASDAQ: MSFT, HKEX: 4338) is an American-based multinational computer technology corporation that develops, manufactures, licenses, and supports a wide range of software products for computing devices.Headquartered in Redmond,
Washington, USA, its most profitable products are the Microsoft Windows operating system and the Microsoft Office suite of productivity software.

Originally founded to develop and sell BASIC interpreters for the Altair 8800, Microsoft rose to dominate the home computer operating system market with MS-DOS in the mid-1980s, followed by the Windows line of operating systems. Its products have all achieved near-ubiquity in the desktop computer market. One commentator notes that Microsoft's original mission was "a computer on every desk and in every home, running Microsoft software." Microsoft possesses footholds in other markets, with assets such as the MSNBC cable television network, the MSN Internet portal, and the Microsoft Encarta multimedia encyclopedia. The company also markets both computer hardware products such as the Microsoft mouse as well as home entertainment
products such as the Xbox, Xbox 360, Zune and MSN TV. The company's initial public stock offering (IPO) was in 1986; the ensuing rise of the company's stock price has made four billionaires and an estimated 12,000 millionaires from Microsoft employees.

Throughout its history the company has been the target of criticism, including monopolistic
business practices and anti-competitive business practices including refusal to deal and tying.
The U.S. Justice Department and the European Commission, among others, have ruled against
Microsoft for various antitrust violations.

Known for what is generally described as a developer-centric business culture, [dubious–discuss] Microsoft has historically given customer support over Usenet newsgroups and the WorldWide Web, and awards Microsoft MVP status to volunteers who are deemed helpful in assisting the company's customers.

1975–1984: Founding

Following the launch of the Altair 8800, William Henry Gates III, (known as Bill Gates) called the creators of the new microcomputer, Micro Instrumentation and Telemetry Systems (MITS), offering to demonstrate an implementation of the BASIC programming language for the system. After the demonstration, MITS agreed to distribute Altair BASIC. Gates left Harvard University, moved to Albuquerque, New Mexico where MITS was located, and founded Microsoft there. The company's first international office was founded on November 1, 1978, in Japan, entitled "ASCII Microsoft" (now called "Microsoft Japan"). On January 1, 1979, the company moved from Albuquerque to a new home in Bellevue, Washington. Steve Ballmer joined the company on June 11, 1980, and later succeeded Bill Gates as CEO.

Among pre-IBM-PC products were the software package TASC (The AppleSoft Compiler), which compiled a BASIC program into Apple machine language, and the hardware Microsoft Softcard, an add-on Z80 processor card for the Apple II and compatible computers which allowed the use of the CP/M operating system instead of Applesoft and Apple DOS.

DOS (Disk Operating System) was the operating system that brought the company its first real success. On August 12, 1981, after negotiations with Digital Research failed, IBM awarded a contract to Microsoft to provide a version of the CP/M operating system, which was set to be used in the upcoming IBM Personal Computer (PC). For this deal, Microsoft purchased a CP/M clone called 86-DOS from Seattle Computer Products, which IBM renamed to PC-DOS. Later, the market saw a flood of IBM PC clones after Columbia Data Products successfully cloned the IBM BIOS, and by aggressively marketing MS-DOS to manufacturers of IBM-PC clones, Microsoft rose from a small player to one of the major software vendors in the home computer industry. The company expanded into new markets with the release of the Microsoft Mouse in 1983, as well as a publishing division named Microsoft Press.

1985–1994: IPO, OS/2 and Windows

In August 1985, Microsoft and IBM partnered in the development of a different operating system called OS/2. On November 20, 1985, Microsoft released its first retail version of Microsoft Windows, originally a graphical extension for its MS-DOS operating system. On March 13, 1986 the company went public with an initial public offering (IPO), with a starting initial offering price of $21.00 and ending at the first day of trading as at US $28.00. The ensuing rise of the stock price has made four billionaires and an estimated 12,000 millionaires from Microsoft employees. In 1987, Microsoft eventually released their first version of OS/2 to OEMs.

IPO

Microsoft's Initial Public Offering occurred on March 14, 1986. The stock closed at $27.75 per share after peaking at $29.25 shortly after the opening. Microsoft's two founders, Gates and Allen, were made instant millionaires. Gates owned 45% of the company's 24.7 million outstanding shares and Allen roughly 25%. Gates' stake was therefore $234 million and Microsoft's total-value $520million, at that time

Post-IPO

In 1989, Microsoft introduced its flagship office suite, Microsoft Office. The software bundled separate office productivity applications, such as Microsoft Word and Microsoft Excel.On May 22, 1990 Microsoft launched Windows 3.0. The new version of Microsoft's operating system boasted such new features as streamlined user interface graphics and improved protected mode capability for the Intel 386 processor; it sold over 100,000 copies in two weeks. Windows at the time generated more revenue for Microsoft than OS/2, and the company decided to move more resources from OS/2 to Windows. In the ensuing years, the popularity of OS/2 declined, and Windows quickly became the favored PC platform.

During the transition from MS-DOS to Windows, the success of Microsoft's product Microsoft Office allowed the company to gain ground on application-software competitors, such as WordPerfect and Lotus 1-2-3. According to The Register, Novell, an owner of WordPerfect for a time, alleged that Microsoft used its inside knowledge of the DOS and Windows kernels and of undocumented Application Programming Interface features to make Office perform better than its competitors. Eventually, Microsoft Office became the dominant business suite, with a market share far exceeding that of its competitors.

In 1993, Microsoft released Windows NT 3.1, a business operating system with the Windows 3.1 user interface but an entirely different kernel.

Versions

Current versions

* Windows Server 2008 for servers.
* Windows Web Server 2008
* Windows Server 2008 Standard Edition
* Windows Server 2008 Enterprise Edition(Microsoft Windows NT 6.0.6001 Service Pack1)
* Windows Server 2008 Datacenter Edition
* Windows Storage Server 2008
* Windows Small Business Server 2008 (Codenamed "Cougar") for small businesses
* Windows Essential Business Server 2008 (Codenamed "Centro") for medium-sized businesses
* Windows Server 2008 for Itanium-based Systems
* Windows HPC Server 2008 for high Performance supercomputers
* Windows Mobile 6.1 for smartphones and PDAs
* Windows Home Server Announced at the 2007 Consumer Electronics Show (CES) in Las Vegas. Windows Home Server is intended to be a solution for homes with multiple connected PCs to offer file sharing, automated backups, and remote access.

* Windows Vista, for home and business desktops and portable computers

.....Windows Vista Starter Much like Windows XP Starter Edition, this edition will be limited to emerging markets such as Colombia, India, Thailand, and Indonesia, mainly to offer a legal alternative to using unauthorized copies. It will not be available in the United States, Canada, Europe, or Australia.

.......Windows Vista Home Basic Similar to Windows XP Home Edition, Home Basic is intended for budget users not requiring advanced media support for home use. The Windows Aero theme with translucent effects will not be included with this edition.

......Windows Vista Home Premium Like Windows XP Media Center Edition, this edition will support more advanced multimedia and entertainment authoring, premium games, mobile and tablet PC support, Network Projector, Windows Aero, Touch Screen, and auxiliary display (via Windows Side Show) support.

...... Vista Business Comparable to Windows XP Professional and Windows XP Tablet PC Edition, Windows Vista Business Edition is aimed at the business market. Includes all the features of Home Premium with the exception of Windows Media Center and related technologies, Parental Controls, and Windows DVD and Movie Maker HD.

....... Vista Enterprise (Microsoft Windows NT 6.0.6000.0) This edition is aimed at the enterprise segment of the market, and is a superset of the Business edition. Additional features include multilingual user interface support, BitLocker Drive Encryption, and UNIX application support. This edition will not be available through retail or OEM channels

....... Vista Ultimate This edition combines all the features of the Home Premium and Enterprise editions, a game performance tweaker (WinSAT), and "Ultimate Extras". On January 7, 2007, at CES, Microsoft began to announce what some of these Ultimate Extras will be.

* Windows XP Embedded, for embedded systems requiring parts of the Windows XP infrastructure
* Windows Fundamentals for Legacy PCs, a low-end version of Windows XP that is intended to be a thin-client that works with older hardware.
* Windows Embedded CE 6.0, for embedded systems (not based on the Windows NT kernel)

Future versions

* Windows 7, slated to be Windows Vista's successor
* Windows Server 2008 R2, slated to be Windows Server 2008's successor

Cancelled versions

* 1999 December - Windows Neptune was sent out to beta testers but was never released. Would have been a consumer version (i.e. home edition) of Windows 2000.
* 1996 May 3 - Windows Nashville (Windows 96) (cancelled) (Became Windows 95B.)
* 1991-1998 - Cairo (a "true object-oriented OS") planned after Windows NT

microsoft logo

What is Hard Disks,and how it works ?

2009-03-28T08:02:00.000-07:00

What is Hard Disk

Nearly every desktop computer and server in use today contains one or more hard-disk drives. Every mainframe and supercomputer is normally connected to hundreds of them. You can even find VCR-type devices and camcorders that use hard disks instead of tape. These billions of hard disks do one thing well -- they store changing digital information in a relatively permanent form. They give computers the ability to remember things when the power goes out.

In this article, we'll take apart a hard disk so that you can see what's inside, and also discuss how they organize the gigabytes of information they hold in files!

Hard Disk Basics

Hard disks were invented in the 1950s. They started as large disks up to 20 inches in diameter holding just a few megabytes. They were originally called "fixed disks" or "Winchesters" (a code name used for a popular IBM product). They later became known as "hard disks" to distinguish them from "floppy disks." Hard disks have a hard platter that holds the magnetic medium, as opposed to the flexible plastic film found in tapes and floppies.

At the simplest level, a hard disk is not that different from a cassette tape. Both hard disks and cassette tapes use the same magnetic recording techniques described in How Tape Recorders Work. Hard disks and cassette tapes also share the major benefits of magnetic storage -- the magnetic medium can be easily erased and rewritten, and it will "remember" the magnetic flux patterns stored onto the medium for many years.

Cassette Tape vs. Hard Disk

Let's look at the big differences between cassette tapes and hard disks:

The magnetic recording material on a cassette tape is coated onto a thin plastic strip. In a hard disk, the magnetic recording material is layered onto a high-precision aluminum or glass disk. The hard-disk platter is then polished to mirror-type smoothness.
With a tape, you have to fast-forward or reverse to get to any particular point on the tape. This can take several minutes with a long tape. On a hard disk, you can move to any point on the surface of the disk almost instantly.
In a cassette-tape deck, the read/write head touches the tape directly. In a hard disk, the read/write head "flies" over the disk, never actually touching it.
The tape in a cassette-tape deck moves over the head at about 2 inches (about 5.08 cm) per second. A hard-disk platter can spin underneath its head at speeds up to 3,000 inches per second (about 170 mph or 272 kph)!
The information on a hard disk is stored in extremely small magnetic domains compared to a cassette tape's. The size of these domains is made possible by the precision of the platter and the speed of the medium.

Because of these differences, a modern hard disk is able to store an amazing amount of information in a small space. A hard disk can also access any of its information in a fraction of a second.

Capacity and Performance

A typical desktop machine will have a hard disk with a capacity of between 10 and 40 gigabytes. Data is stored onto the disk in the form of files. A file is simply a named collection of bytes. The bytes might be the ASCII codes for the characters of a text file, or they could be the instructions of a software application for the computer to execute, or they could be the records of a data base, or they could be the pixel colors for a GIF image. No matter what it contains, however, a file is simply a string of bytes. When a program running on the computer requests a file, the hard disk retrieves its bytes and sends them to the CPU one at a time.

There are two ways to measure the performance of a hard disk:

Data rate - The data rate is the number of bytes per second that the drive can deliver to the CPU. Rates between 5 and 40 megabytes per second are common.
Seek time - The seek time is the amount of time between when the CPU requests a file and when the first byte of the file is sent to the CPU. Times between 10 and 20 milliseconds are common.

The other important parameter is the capacity of the drive, which is the number of bytes it can hold.

Inside: Electronics Board

The best way to understand how a hard disk works is to take a look inside. (Note that OPENING A HARD DISK RUINS IT, so this is not something to try at home unless you have a defunct drive.)

Here is a typical hard-disk drive:

It is a sealed aluminum box with controller electronics attached to one side. The electronics control the read/write mechanism and the motor that spins the platters. The electronics also assemble the magnetic domains on the drive into bytes (reading) and turn bytes into magnetic domains (writing). The electronics are all contained on a small board that detaches from the rest of the drive:
Inside: Beneath the Board

Underneath the board are the connections for the motor that spins the platters, as well as a highly-filtered vent hole that lets internal and external air pressures equalize:

Removing the cover from the drive reveals an extremely simple but very precise interior:
In this picture you can see:

The platters - These typically spin at 3,600 or 7,200 rpm when the drive is operating. These platters are manufactured to amazing tolerances and are mirror-smooth (as you can see in this interesting self-portrait of the author... no easy way to avoid that!).
The arm - This holds the read/write heads and is controlled by the mechanism in the upper-left corner. The arm is able to move the heads from the hub to the edge of the drive. The arm and its movement mechanism are extremely light and fast. The arm on a typical hard-disk drive can move from hub to edge and back up to 50 times per second -- it is an amazing thing to watch!

Inside: Platters and Heads

In order to increase the amount of information the drive can store, most hard disks have multiple platters. This drive has three platters and six read/write heads:

The mechanism that moves the arms on a hard disk has to be incredibly fast and precise. It can be constructed using a high-speed linear motor.

Many drives use a "voice coil" approach -- the same technique used to move the cone of a speaker on your stereo is used to move the arm.

Storing the Data

Data is stored on the surface of a platter in sectors and tracks. Tracks are concentric circles, and sectors are pie-shaped wedges on a track, like this:

A typical track is shown in yellow; a typical sector is shown in blue. A sector contains a fixed number of bytes -- for example, 256 or 512. Either at the drive or the operating system level, sectors are often grouped together into clusters.

The process of low-level formatting a drive establishes the tracks and sectors on the platter. The starting and ending points of each sector are written onto the platter. This process prepares the drive to hold blocks of bytes. High-level formatting then writes the file-storage structures, like the file-allocation table, into the sectors. This process prepares the drive to hold files.

What are .INF files ??

2009-03-26T05:30:00.000-07:00

INF file

An INF file (or Setup Information file) is a plain text file used by Microsoft Windows for installation of software and drivers. INF files are most commonly used for installing device drivers for hardware components. Windows includes IExpress.exe for the creation of INF-based installations. INF files are part of the Windows Setup API.

Structure of an INF file

The structure of an INF file is very similar to that of an INI file; it contains various sections that specify the files to be copied, changes to the registry etc. All INF files contain a [version] section with a Signature value specifying the version of Windows that the INF file is meant for. The signature is commonly $CHICAGO$ (for Windows 9x) or $WINDOWS NT$ (for Windows NT/2K/XP) Most of the remaining sections are user-defined and contain information specific to the component being installed.

Purpose of .INF Files

Ask just about any device driver writer, "What is the worst part of writing Windows device drivers?" and most will reply, "Writing .INF files!" The reason for this is that the documentation on .INF files in the DDK has not provided a procedural approach to describing .INF files, such as, "If you want to accomplish X, then do Y followed by Z".

This article will describe the basics of .INF files and how they are used in the installation of a device driver.

An .INF file can do many things; however, 97% of all .INF files really only perform three tasks:

1.)Identify the driver for a particular device. This is done using one or more Hardware IDs or Compatible IDs. The system device installer will take the Hardware IDs and Compatible IDs that were reported for a device (by its bus driver), and try and find an exact character for character match in an .INF file. When a match is found, then the system device installer knows that the .INF file describes the driver(s) for the device.

2.)Copy files from the installation medium to the system. In addition to the driver binary (the .SYS file), driver packages may also include DLLs, co-installers, applications, or any other type of file.

3.)Add entries to the registry. This describes the device and its relationship to other devices, provides for device or driver specific configuration information, and describes the driver "service" to the service control manager.

Thats it. Sounds simple, doesnt it? Actually, it is pretty simple (no, Im not kidding!).

"Youre right", replied the little bear, "even a Bear of Little Brain understands that"

The two most confusing aspects of .INF files are usually:

1.)The .INF file is not 'run from the beginning to the end; individual sections in the .INF file are 'run based upon the phase of the installation process.

2.)Most of the sections in the .INF file are actually part of a well-defined hierarchy. This fact is obscured by the squashing of the hierarchy into a flat text file.

Creating International INF Files

An INF that will be used in an international market should use %strkey% tokens for all user-viewable text. The string tokens are defined in a [Strings] section, which is typically at the end of the INF file.

To create a single international INF file, the INF can have a set of locale-specific Strings.LanguageID sections, as described in the reference page for the INF Strings Section in the Windows 2000 DDK documentation.

Alternatively, you can create a separate INF for each locale. To reduce duplication and ease maintenance, you can create a main INF file with all the necessary sections and entries, except for the Strings section. Then create a second set of files, where each file contains just the Strings section for a supported locale. Concatenate the main file with each strings file to generate the locale-specific INF files.

If an INF contains characters outside the ASCII range (outside the range 0-127), the INF should be in Unicode format. To create such a file, for example, save the INF as a Unicode file from an application like Notepad. If the INF is not in Unicode format, Setup uses the current locale to translate characters. If the INF is in Unicode format, Setup uses the full character set.

commonly used sections

General Syntax Rules for INF Files

An INF file is a text file organized into named sections. Some sections have system-defined names and some sections have names determined by the writer of the INF file.

Each section contains section-specific entries, which are interpreted by Setup software (class installers, co-installers, SetupAPI). Some entries begin with a predefined keyword. These entries are called directives.

Some INF file entries are essentially pointers from one section to another, for a specific purpose. For example, an INF AddReg directive identifies a section containing entries that instruct Setup to modify the registry. These entries sometimes include additional arguments (required or optional) for Setup to interpret during installation.

Other INF file entries do not point to other sections, but simply supply information that Setup uses during installation, such as file names, registry values, hardware configuration information, flags, and so on. For example, an INF DriverVer directive supplies driver version information.

When Setup begins an installation, it first looks for an INF Version section to verify the validity of the INF file and to determine where installation files are located. It then starts the installation by finding an INF Manufacturer section, which will contain directives to INF Models sections, which in turn provide directives leading to various INF DDInstall sections, based on the hardware ID of the device being installed.

The following syntax rules govern the required and optional contents of INF files, the format of section names by using string tokens, and line format, continuation, and comments.

Sample INF File

The following is a sample INF file that demonstrates the syntax understood by the Internet Component Download service.

_________________________

;Sample INF file for CIRC3.OCX
[Add.Code]
circ3.ocx=circ3.ocx
random.dll=random.dll
mfc40.dll=mfc40.dll
example.ocx=example.ocx

[circ3.ocx]
; Lines below specify that the specified circ3.ocx (clsid, version)
; needs to be installed on the system. If it doesn't exist already,
; it can be downloaded from the given location (a .cab file).
; Note: if "thiscab" is specified instead of the file location,
; it is assumed that the desired file is present in the same .cab
; cabinet that the INF originated from. Otherwise, if the location
; pointed to is a different .cab, the new cabinet is also downloaded
; and unpacked in order to extract the desired file.
file=http://www.code.com/circ3/circ3.cab
clsid={9DBAFCCF-592F-101B-85CE-00608CEC297B}
; Note that the {}s are required when entering a in the INF file.
; This is slightly different from the HTML syntax for inserting CLSIDs
; in an tag.
FileVersion=1,0,0,143

[random.dll]
; Lines below specify that the random.dll needs to be installed in
; the system.
; If this doesn't exist already, it can be downloaded from the given
; location.
file=http:// www.code.com/circ3/random.dll
; Note that the FileVersion is optional, and it can also be left
; empty, meaning that any version is ok.
FileVersion=
DestDir=10

; DestDir can be set to 10 or 11 ( LDID_WIN or LDID_SYS by INF
; convention).
; This places files in \Windows or \Windows\System, respectively.
; If no dest dir is specified (typical case), code is installed in
; the occache directory.

[mfc40.dll]
; Leaving the file location empty specifies that the installation
; needs mfc40 (version 4,0,0,5), but it should not be downloaded.
; If this file is not already present on the client machine, component
; download fails.
file=
FileVersion=4,0,0,5

[example.ocx]
; Leaving the file location empty specifies that the installation
; needs the specified example.ocx (clsid, version), but it should not
; be downloaded.
; If this file is not already present on the client machine, component
; download fails.
file=clsid={DEADBEEF-592F-101B-85CE-00608CEC297B}
FileVersion=1,0,0,143

_______________________

Order of Processing and Execution of INF Files

The [Add.Code] section is processed in the order listed, but the files are installed and set up in reverse order. This means that typically you would list the main OCX file first in the INF file, followed by dependent DLLs. The dependent DLLs are guaranteed to be installed and available at registration time of the main OCX.

Unconditional hooks, those hooks in the [Setup Hooks] section in the INF file, are executed in the order listed in that section (Hook1 executes before Hook2). Conditional hooks, those hooks in the file sections referenced by file names in the [Add.Code] section, are executed in the order of the [Add.Code] section. Between conditional hooks and file section installation/setup, conditional hooks always get executed before file section installations/setups in the same .cab file. Between two file section installations/setups, the order of file installation and setup is the reverse of the listing in the [Add.Code] section. Between two conditional hooks, the order is the same as that listed in the [Add.Code] section. Note this different ordering rule between conditional hooks and file section installation and setup.

INF Size Limits

* A Windows 9x/Me INF file cannot be larger than 64 kilobytes. There is no practical limit to the size of an INF file for NT-based systems.
* The maximum length, in characters, of an INF file field, before string substitution and including a terminating NULL character, is 4096 (Windows Vista and later versions of Windows) and 512 (Windows Server 2003, Windows XP, and Windows 2000).
* After string substitution, the maximum length, in characters, of an INF file string is 4096, including a terminating NULL character.
* Note, however, that Plug and Play may impose a more restrictive limit for certain INF file fields that it recognizes or uses, such as device description, driver provider, and device manufacturer.

Autorun.inf, What is it?

Autorun.inf is the primary instruction file associated with the Autorun function. Autorun.inf itself is a simple text-based configuration file that tells the operating system which executable to start, which icon to use, and which additional menu commands to make available. In other words, autorun.inf Windows how to deal open the presentation and treat the contents of the CD.

The entire sequence is initiated when the "disk change notifcation" polling discovers a new disk in the CD or DVD ROM drive. Then, if the "Auto insert notification" feature is enabled (it is by default), Windows checks in the new disk's root directory for the existence of an "autorun.inf" file. If found, Windows then reads and follows the specific instructions this file defines. If no autorun.inf file is found, then Windows refers to the new disk by its serial number and executes the default actions associated with the (data or audio) content on the disk.

Autorun.inf Defines the following:

**The process or application that will automatically run when a disk is inserted Automatically run when CD is inserted
**Optionally, one can define the process or application that will run for specific Operating environments. Icon Representing CD or DVD
**The icon that will represent your application's CD or DVD when the drive is viewed with My Computer or Explorer.
**Menu Commands when CD-ROM is clicked Menu commands displayed when the user right-clicks the CD-ROM icon from My Computer or Explorer.

A simple Autorun.inf example:

[autorun]
open=autorun.exe
icon=autorun.ico

A complex Autorun.inf example:

This example is used in the following section for complete definition and descriptions.
________________________________________

[autorun]
open=filename.exe /argument1
icon=\foldername\filename.dll,5
[autorun.mips]
open=filenam2.exe
icon=filename.ico
[autorun.alpha]
open=filenam3.exe
icon=filename.ico
[autorun.ppc]
open=filenam4.exe
icon=filename.ico
shell\install = &Install
shell\install\command = setup.exe
shell\uninstall = &UnInstall
shell\uninstall\command = Uninstall.exe
shell\readme = &Read Me
shell\readme\command = notepad readme.txt
shell\help = &Help
shell\help\command = helpfilename.hlp

_________________________________________

Example Autorun File: Description:

[autorun]	[autorun] is the primary, required section name.
open=filename.exe /argument1	Open is the keyword to determine what action to take upon insert notification.
	filename.exe is the value defining the application that will be automatically started.
	/argument1 is the argument, parameter or switch passed to the application being run. Logically, any command line parameters used must be supported by the application.
icon=\foldername\filename.dll,5	Icon is the keyword to determine the icon used for the disk.
	filename.dll is the value defining the file containing the icon.
	,5 is the argument to the icon resource defining which icon to display.

Note: By default, the system looks for the file in the root directory of the inserted disk. If you want to access a file located in a specific folder or subdirectory, specify a path relative to the root.

Example: open = foldername\filename.exe This will not change the current directory.

Although AutoPlay is the default menu item, you can define a different command to be the default by including the following line. shell = verb

When the user double-clicks on the icon, the command associated with this entry will be carried out.
Note: a more common method of defining the icon resouce is an explicit reference to a .ico file. Example: icon=autorun.ico

Note: The icon defined representing your application's CD or DVD is the drive icon as viewed with My Computer or Explorer. Valid file types containing icons include .ICO .BMP .EXE .DLL If the file includes more than one icon, by default, the second icon in the files icon resource will be displayed.

Example Autorun File: Description:

[autorun.mips]	Defining the autorun items for a mips machine
open=filenam2.exe	The platform specific application to run
icon=filename2.ico	The platform specific autorun icon
[autorun.alpha]	Defining the autorun items for a DEC Alphamachine
open=filenam3.exe	The platform specific application to run
icon=filename3.ico	The platform specific autorun icon
[autorun.ppc]	Defining the autorun items for a Power PC
open=filenam4.exe	The platform specific application to run
icon=filename4.ico	The platform specific autorun icon
shell\install = &Install	The Keyword defining a menu item and the Hot key for that item
shell\install\command = setup.exe	The keyword defining the operation to perform when the user selects this item
shell\uninstall = &UnInstall	Additional menu item example
shell\uninstall\command = Uninstall.exe	Additional menu item example
shell\readme = &Read Me	Additional menu item example
shell\readme\command = notepad readme.txt	Additional menu item example
shell\help = &Help	Additional menu item example
shell\help\command = helpfilename.hlp	Additional menu item example

About Internet search engine

2009-03-22T03:07:00.000-07:00

Introduction:

The good news about the Internet and its most visible component, the World Wide Web, is that there are hundreds of millions of pages available, waiting to present information on an amazing variety of topics. The bad news about the Internet is that there are hundreds of millions of pages available, most of them titled according to the whim of their author, almost all of them sitting on servers with cryptic names. When you need to know about a particular subject, how do you know which pages to read? If you're like most people, you visit an Internet search engine.

Internet search engines are special sites on the Web that are designed to help people find information stored on other sites. There are differences in the ways various search engines work, but they all perform three basic tasks:

They search the Internet -- or select pieces of the Internet -- based on important words.
They keep an index of the words they find, and where they find them.
They allow users to look for words or combinations of words found in that index.

Early search engines held an index of a few hundred thousand pages and documents, and received maybe one or two thousand inquiries each day. Today, a top search engine will index hundreds of millions of pages, and respond to tens of millions of queries per day.

Looking at the web:

Before a search engine can tell you where a file or document is, it must be found. To find information on the hundreds of millions of Web pages that exist, a search engine employs special software robots, called spiders, to build lists of the words found on Web sites. When a spider is building its lists, the process is called Web crawling.

In order to build and maintain a useful list of words, a search engine's spiders have to look at a lot of pages.

How does any spider start its travels over the Web? The usual starting points are lists of heavily used servers and very popular pages. The spider will begin with a popular site, indexing the words on its pages and following every link found within the site. In this way, the spidering system quickly begins to travel, spreading out across the most widely used portions of the Web.

Each spider could keep about 300 connections to Web pages open at a time. At its peak performance, using four spiders, their system could crawl over 100 pages per second, generating around 600 kilobytes of data each second.

When the Google spider looked at an HTML page, it took note of two things:

The words within the page
Where the words were found

Words occurring in the title, subtitles, meta tags and other positions of relative importance were noted for special consideration during a subsequent user search. The Google spider was built to index every significant word on a page, leaving out the articles "a," "an" and "the." Other spiders take different approaches.

These different approaches usually attempt to make the spider operate faster, allow users to search more efficiently, or both. For example, some spiders will keep track of the words in the title, sub-headings and links, along with the 100 most frequently used words on the page and each word in the first 20 lines of text. Lycos is said to use this approach to spidering the Web.

Other systems, such as AltaVista, go in the other direction, indexing every single word on a page, including "a," "an," "the" and other "insignificant" words. The push to completeness in this approach is matched by other systems in the attention given to the unseen portion of the Web page, the meta tags.

Meta tags:

Meta tags allow the owner of a page to specify key words and concepts under which the page will be indexed. This can be helpful, especially in cases in which the words on the page might have double or triple meanings -- the meta tags can guide the search engine in choosing which of the several possible meanings for these words is correct. There is, however, a danger in over-reliance on meta tags, because a careless or unscrupulous page owner might add meta tags that fit very popular topics but have nothing to do with the actual contents of the page. To protect against this, spiders will correlate meta tags with page content, rejecting the meta tags that don't match the words on the page.

Building the index:

Once the spiders have completed the task of finding information on Web pages (and we should note that this is a task that is never actually completed -- the constantly changing nature of the Web means that the spiders are always crawling), the search engine must store the information in a way that makes it useful. There are two key components involved in making the gathered data accessible to users:

The information stored with the data
The method by which the information is indexed

In the simplest case, a search engine could just store the word and the URL where it was found. In reality, this would make for an engine of limited use, since there would be no way of telling whether the word was used in an important or a trivial way on the page, whether the word was used once or many times or whether the page contained links to other pages containing the word. In other words, there would be no way of building the ranking list that tries to present the most useful pages at the top of the list of search results.

To make for more useful results, most search engines store more than just the word and URL. An engine might store the number of times that the word appears on a page. The engine might assign a weight to each entry, with increasing values assigned to words as they appear near the top of the document, in sub-headings, in links, in the meta tags or in the title of the page. Each commercial search engine has a different formula for assigning weight to the words in its index. This is one of the reasons that a search for the same word on different search engines will produce different lists, with the pages presented in different orders.

Regardless of the precise combination of additional pieces of information stored by a search engine, the data will be encoded to save storage space. For example, the original Google paper describes using 2 bytes, of 8 bits each, to store information on weighting -- whether the word was capitalized, its font size, position, and other information to help in ranking the hit. Each factor might take up 2 or 3 bits within the 2-byte grouping (8 bits = 1 byte). As a result, a great deal of information can be stored in a very compact form. After the information is compacted, it's ready for indexing.

An index has a single purpose: It allows information to be found as quickly as possible. There are quite a few ways for an index to be built, but one of the most effective ways is to build a hash table. In hashing, a formula is applied to attach a numerical value to each word. The formula is designed to evenly distribute the entries across a predetermined number of divisions. This numerical distribution is different from the distribution of words across the alphabet, and that is the key to a hash table's effectiveness.

In English, there are some letters that begin many words, while others begin fewer. You'll find, for example, that the "M" section of the dictionary is much thicker than the "X" section. This inequity means that finding a word beginning with a very "popular" letter could take much longer than finding a word that begins with a less popular one. Hashing evens out the difference, and reduces the average time it takes to find an entry. It also separates the index from the actual entry. The hash table contains the hashed number along with a pointer to the actual data, which can be sorted in whichever way allows it to be stored most efficiently. The combination of efficient indexing and effective storage makes it possible to get results quickly, even when the user creates a complicated search.

Building a search:

Searching through an index involves a user building a query and submitting it through the search engine. The query can be quite simple, a single word at minimum. Building a more complex query requires the use of Boolean operators that allow you to refine and extend the terms of the search.

The Boolean operators most often seen are:

AND - All the terms joined by "AND" must appear in the pages or documents. Some search engines substitute the operator "+" for the word AND.
OR - At least one of the terms joined by "OR" must appear in the pages or documents.
NOT - The term or terms following "NOT" must not appear in the pages or documents. Some search engines substitute the operator "-" for the word NOT.
FOLLOWED BY - One of the terms must be directly followed by the other.
NEAR - One of the terms must be within a specified number of words of the other.
Quotation Marks - The words between the quotation marks are treated as a phrase, and that phrase must be found within the document or file.

What is WIKI ??

2009-03-22T02:52:00.000-07:00

A wiki is a page or collection of Web pages designed to enable anyone who accesses it to contribute or modify content (excluding blocked users), using a simplified markup language. Wikis are often used to create collaborative websites and to power community websites. The collaborative encyclopedia Wikipedia is one of the best-known wikis. Wikis are used in business to provide intranet and knowledge management systems. Ward Cunningham, the developer of the first wiki software, WikiWikiWeb, originally described it as "the simplest online database that could possibly work." "Wiki" (/wiːkiː/) is a Hawaiian word for "fast". "Wiki Wiki" is a reduplication. "Wiki" can be expanded as "What I Know Is," but this is a backronym.

History of WIKI

WikiWikiWeb was the first site to be called a wiki. Ward Cunningham started developing WikiWikiWeb in 1994, and installed it on the Internet domain c2.com on March 25, 1995. It was named by Cunningham, who remembered a Honolulu International Airport counter employee telling him to take the "Wiki Wiki" shuttle bus that runs between the airport's terminals. According to Cunningham, "I chose wiki-wiki as an alliterative substitute for 'quick' and thereby avoided naming this stuff quick-web." Cunningham was in part inspired by Apple's HyperCard. Apple had designed a system allowing users to create virtual "card stacks" supporting links among the various cards. developed CunninghamVannevar Bush's ideas by allowing users to "comment on and change one another's text". In the early 2000s, wikis were increasingly adopted in enterprise as collaborative software. Common uses included project communication, intranets, and documentation, initially for technical users. Today some companies use wikis as their only collaborative software and as a replacement for static intranets. There may be greater use of wikis behind firewalls than on the public Internet.

Characteristics of WIKI :

Ward Cunningham, and co-author Bo Leuf, in their book The Wiki Way: Quick Collaboration on the Web described the essence of the Wiki concept as follows:

* A wiki invites all users to edit any page or to create new pages within the wiki Web site, using only a plain-vanilla Web browser without any extra add-ons.

* Wiki promotes meaningful topic associations between different pages by making page link creation almost intuitively easy and showing whether an intended target page exists or not.

* A wiki is not a carefully crafted site for casual visitors. Instead, it seeks to involve the visitor in an ongoing process of creation and collaboration that constantly changes the Web site landscape.

* A wiki enables documents to be written collaboratively, in a simple markup language using a Web browser. A single page in a wiki website is referred to as a "wiki page", while the entire collection of pages, which are usually well interconnected by hyperlinks, is "the wiki". A wiki is essentially a database for creating, browsing, and searching through information.

A defining characteristic of wiki technology is the ease with which pages can be created and updated. Generally, there is no review before modifications are accepted. Many wikis are open to alteration by the general public without requiring them to register user accounts. Sometimes logging in for a session is recommended, to create a "wiki-signature" cookie for signing edits automatically. Many edits, however, can be made in real-time and appear almost instantly online. This can facilitate abuse of the system. Private wiki servers require user authentication to edit pages, and sometimes even to read them.

Editing WIKI Pages

Ordinarily, the structure and formatting of wiki pages are specified with a simplified markup language, sometimes known as "wikitext". For example, starting a line of text with an asterisk ("*") is often used to enter it in a bulleted list. The style and syntax of wikitexts can vary greatly among wiki implementations, some of which also allow HTML tags.

The reason for taking this approach is that HTML, with its many cryptic tags, is not very legible, making it hard to edit. Wikis therefore favour plain text editing, with fewer and simpler conventions than HTML, for indicating style and structure.

Although limiting access to HTML and cascading style sheets (CSS) of wikis limits user ability to alter the structure and formatting of wiki content, there are some benefits. Limited access to CSS promotes consistency in the look and feel and having JavaScript disabled prevents a user from implementing code, which may limit access for other users.

Increasingly, wikis are making "WYSIWYG" ("What You See Is What You Get") editing available to users, usually by means of JavaScript or an ActiveX control that translates graphically entered formatting instructions, such as "bold" and "italics", into the corresponding HTML tags or wikitext. In those implementations, the markup of a newly edited, marked-up version of the page is generated and submitted to the server transparently, and the user is shielded from this technical detail. However, WYSIWYG controls do not always provide all of the features available in wikitext.

Many implementations (for example MediaWiki) allow users to supply an "edit summary" when they edit a page. This is a short piece of text (usually one line) summarizing the changes. It is not inserted into the article, but is stored along with that revision of the page, allowing users to explain what has been done and why; this is similar to a log message when committing changes to a revision control system. Most wikis keep a record of changes made to wiki pages; often every version of the page is stored. This means that authors can revert to an older version of the page, should it be necessary because a mistake has been made or the page has been vandalized.

Navigation

Within the text of most pages there are usually a large number of hypertext links to other pages. This form of non-linear navigation is more "native" to wiki than structured/formalized navigation schemes. That said, users can also create any number of index or table of contents pages, with hierarchical categorization or whatever form of organization they like. These may be challenging to maintain by hand, as multiple authors create and delete pages in an ad hoc manner. Wikis generally provide one or more ways to categorize or tag pages to support the maintenance of such index pages.

Most wikis have a backlink feature, which displays all pages that link to a given page. It is typical in a wiki to create links to pages that do not yet exist, as a way to invite others to share what they know about a subject new to the wiki.

Linking and creating pages

Links are created using a specific syntax, the so-called "link pattern" (also see CURIE).

Originally, most wikis used CamelCase to name pages and create links. These are produced by capitalizing words in a phrase and removing the spaces between them (the word "CamelCase" is itself an example). While CamelCase makes linking very easy, it also leads to links which are written in a form that deviates from the standard spelling. CamelCase-based wikis are instantly recognizable because they have many links with names such as "TableOfContents" and "BeginnerQuestions." It is possible for a wiki to render the visible anchor for such links "pretty" by reinserting spaces, and possibly also reverting to lower case. However, this reprocessing of the link to improve the readability of the anchor is limited by the loss of capitalization information caused by CamelCase reversal. For example, "RichardWagner" should be rendered as "Richard Wagner," whereas "PopularMusic" should be rendered as "popular music." There is no easy way to determine which capital letters should remain capitalized. As a result, many wikis now have "free linking" using brackets, and some disable CamelCase by default.

Searching

Most wikis offer at least a title search, and sometimes a full-text search. The scalability of the search depends on whether the wiki engine uses a database. Indexed database access is necessary for high speed searches on large wikis. Alternatively, external search engines such as Google can sometimes be used on wikis with limited searching functions in order to obtain more precise results. However, a search engine's indexes can be very out of date (days, weeks or months) for many websites.

WIKI uses :

In entertainment

* WIKI (computer game), a 2006 massively multiplayer online role-playing game
* WIKI (FM) a country music radio station in Carrollton, Kentucky, United States
* Wiki Dankowska, a fictional character
* Wiki, a sidekick character in the video game Zack & Wiki: Quest for Barbaros' Treasure
* Wiki Wiki, a phrase made popular in "Wild Wild West" (Will Smith song)
* W1K1, pronounced "wiki", a mini-robot from the 1970s Filmation sci-fi show Jason of Star Command
* Vicky the Viking (also Wikki or Wickie), a 1970s animated cartoon character
* Loeki, Rieki, Wieki, three living dolls from a series of story-albums (singles) for children, sold with Biotex detergent in the early seventies.

Other uses:

* Wiki wiki dollar, a 1960s gasoline give-away promotion
* Wiki Wiki Shuttle, a Hawaiian airport bus system
* WikiWikiWeb, the original wiki website (about computer programming)

What is wiki ---Video

some of the WIKI sites:

About Adobe an Macromedia Flash

2009-03-21T08:29:00.000-07:00

What is FLASH

Adobe Flash (previously called Macromedia Flash) is a multimedia platform originally acquired by Macromedia and currently developed and distributed by Adobe Systems. Since its introduction in 1996, Flash has become a popular method for adding animation and interactivity to web pages; Flash is commonly used to create animation, advertisements, and various web page components, to integrate video into web pages, and more recently, to develop rich Internet applications.

A simple flash document

Flash can manipulate vector and raster graphics and supports bi-directional streaming of audio and video. It contains a scripting language called ActionScript. Several software products, systems, and devices are able to create or display Flash content, including Adobe Flash Player, which is available for most common web browsers, some mobile phones and other electronic devices (using Flash Lite). The Adobe Flash Professional multimedia authoring program is used to create content for the Adobe Engagement Platform, such as web applications, games and movies, and content for mobile phones and other embedded devices.

Files in the SWF format, traditionally called "ShockWave Flash" movies, "Flash movies" or "Flash games", usually have a '.swf ' file extension and may be an object of a web page, strictly "played" in a standalone Flash Player, or incorporated into a Projector, a self-executing Flash movie (with the .exe extension in Microsoft Windows). Flash Video (FLV) files have a .flv file extension and are either used from within .swf files or played through a flv aware player, such as VLC, or QuickTime and Windows Media Player with external codecs added.

History Of FLASH

The program Flash was the Brainchild of Jonathan Gay, who developed the idea while in college and extended it while working for Silicon Beach Software and its successors.

In January 1993, Jonathan Gay, Charlie Jackson, and Michelle Welsh started a small software company called FutureWave Software and created their first product, SmartSketch. A drawing application for pen computers running the PenPoint OS, SmartSketch was designed to make creating computer graphics as simple as drawing on paper. When PenPoint failed in the marketplace, SmartSketch was ported to Microsoft Windows and Mac OS. As the Internet began to thrive, however, FutureWave began to realize the potential for a vector-based web animation tool that might easily challenge Macromedia's Shockwave technology. In 1995, FutureWave modified SmartSketch by adding frame-by-frame animation features and re-released it as FutureSplash Animator on Macintosh and PC. By that time, the company had added a second programmer Robert Tatsumi, artist Adam Grofcsik, and PR specialist Ralph Mittman. Tatsumi focused on writing the authoring tool's user interface, while Gay wrote the graphics renderer, curve and shape math code and the browser plug-in. The product was offered to Adobe and used by Microsoft in its early work with the Internet (MSN). In December 1996, Macromedia acquired the vector-based animation software and later released it as Flash, contracting "Future" and "Splash" of the FutureWave name.

Versions of Flash Released in past:

1.) FutureSplash Animator (April 10, 1996): initial version of Flash with basic editing tools and a timeline

2.) Macromedia Flash 1 (November 1996): a Macromedia re-branded version of the FutureSplash Animator

3.) Macromedia Flash 2 (June 1997): Released with Flash Player 2, new features included: the object library

4.) Flash 3 (May 31, 1998): Released with Flash Player 3, new features included: the movieclip element, JavaScript plug-in integration, transparency and an external stand alone player

5.) Macromedia Flash 4 (June 15, 1999): Released with Flash Player 4, new features included: internal variables, an input field, advanced ActionScript, and streaming MP3

6.) Macromedia Flash 5 (August 24, 2000): Released with Flash Player 5, new features included: ActionScript 1.0 (based on ECMAScript, making it very similar to JavaScript in syntax), XML support, Smartclips (the precursor to components in Flash), HTML text formatting added for dynamic text

7.) Flash MX (ver 6) (March 15, 2002): Released with Flash Player 6, new features included: a video codec (Sorenson Spark), Unicode, v1 UI Components, compression, ActionScript vector drawing API

8.) Macromedia Flash MX 2004 (ver 7) (September 9, 2003): Released with Flash Player 7, new features included: Actionscript 2.0 (which enabled an object-oriented programming model for Flash)(although it lacked the Script assist function of other versions, meaning Actionscript could only be typed out manually), behaviors, extensibility layer (JSAPI), alias text support, timeline effects

9.)Macromedia Flash MX Professional 2004 (ver 7) (September 9, 2003): Released with Flash Player 7, new features included all Flash MX 2004 features plus: Screens (forms for non-linear state-based development and slides for organizing content in a linear slide format like PowerPoint), web services integration, video import wizard, Media Playback components (which encapsulate a complete MP3 and/or FLV player in a component that may be placed in an SWF), Data components (DataSet, XMLConnector, WebServicesConnector, XUpdateResolver, etc) and data binding APIs, the Project Panel, v2 UI components, and Transition class libraries.

10.) Macromedia Flash 8:

1.)Macromedia Flash Basic 8 (released on September 13, 2005): A less feature-rich version of the Flash authoring tool targeted at new users who only want to do basic drawing, animation and interactivity. Released with Flash Player 8, this version of the product has limited support for video and advanced graphical and animation effects.
2.) Macromedia Flash Professional 8 (released on September 13, 2005): Released with the Flash Player 8, Flash Professional 8 added features focused on expressiveness, quality, video, and mobile authoring. New features included Filters and blend modes, easing control for animation, enhanced stroke properties (caps and joins), object-based drawing mode, run-time bitmap caching, FlashType advanced anti-aliasing for text, On2 VP6 advanced video codec, support for alpha transparency in video, a stand-alone encoder and advanced video importer, cue point support in FLV files, an advanced video playback component, and an interactive mobile device emulator.

11.) Flash CS3 Professional (as version 9, released on April 16, 2007): Flash CS3 is the first version of Flash released under the Adobe name. CS3 features full support for ActionScript 3.0, allows things to be converted into ActionScript, adds better integration with other Adobe products such as Adobe Photoshop, and also provides better Vector drawing behavior, becoming more like Adobe Illustrator and Adobe Fireworks.

12.) Adobe Flash CS4 Professional (as version 10, released on October 15, 2008): Contains inverse kinematics (bones), basic 3D object manipulation, object-based animation, an enhanced text engine, and further expansions to ActionScript 3.0.

Recent developments

Adobe Labs (previously Macromedia Labs) is a source for news and pre-release versions of emerging products and technologies from Adobe. Most innovations, such as Flash 9, Flex 3, and ActionScript 3.0 have all been discussed and/or trialled on the site. One area Adobe is focusing on (as of February 2009) is the deployment Rich InternetApplications (RIAs). To this end, they released Adobe Integrated Runtime (AIR), a cross-platform runtime environment which can be used to build, using Adobe Flash, rich Internet applications that can be deployed as a desktop application. It recently surpassed 100 million installations worldwide. Two additional components designed for large scale implementation have been proposed by Adobe for future releases of Flash. First the option to require an ad to be played in full before the main video piece is played. Secondly, Adobe has announced plans to add Digital Rights Management (DRM) capabilities into the new version of Flash. This way Adobe can give companies the option to link an advertisement with content and make sure that both are played and that they not be changed. The current status of these two projects is unclear. [dated info] Flash Player for smartphones is expected to be available to handset manufacturers at the end of 2009.

Format and plug-in

Compared to other plug-ins such as Java, Acrobat Reader, QuickTime, or Windows Media Player, the Flash Player has a small install size, quick download time, and fast initialization time. However, care must be taken to detect and embed the Flash Player in (X)HTML in a W3C compliant way.
In addition to a vector-rendering engine, the Flash Player includes a virtual machine called the ActionScript Virtual Machine (AVM) for scripting interactivity at run-time, support for video, MP3-based audio, and bitmap graphics.

As of Flash Player 8, it offers two video codecs:

On2 Technologies VP6 and Sorenson Spark, and run-time support for JPEG, Progressive JPEG, PNG, and GIF. In the next version, Flash is slated to use a just-in-time compiler for the ActionScript engine.

Use of computer resources

1.) It is argued that the performance of Adobe Flash Player on different platforms may not be optimal.
2.) Any flash player has to be able to animate on top of the video rendering, which makes hardware accelerated video rendering at least not as straightforward as with a purpose built multimedia player.[41] It is not uncommon for other multimedia players to play fine where Flash Player drops frames and skips audio.

Many popular web browsers now have extensions that prevent immediate Flash playback, but lets the user play it by clicking it first. Firefox has NoScript and Flashblock while a separate extension for Opera called Flashblock is available. One similar extension for Internet Explorer is Foxie, and contains a number of features, one of which is also named Flashblock. K-Meleon has a built-in Flash blocker.

PHP language and its History

2009-03-20T08:44:00.000-07:00

what is PHP

PHP is a scripting language originally designed for producing dynamic web pages. It has evolved to include a command line interface capability and can be used in standalone graphical applications.

While PHP was originally created by Rasmus Lerdorf in 1995, the main implementation of PHP is now produced by The PHP Group and serves as the de facto standard for PHP as there is no formal specification.PHP is free software released under the PHP License, however it is incompatible with the GNU General Public License (GPL), due to restrictions on the usage of the term PHP.

PHP is a widely-used general-purpose scripting language that is especially suited for web development and can be embedded into HTML. It generally runs on a web server, taking PHP code as its input and creating web pages as output. It can be deployed on most web servers and on almost every operating system and platform free of charge. PHP is installed on more than 20 million websites and 1 million web servers.

History of PHP

PHP originally stood for Personal Home Page. It began in 1994 as a set of Common Gateway Interface binaries written in the C programming language by the Danish/Greenlandic programmer Rasmus Lerdorf. Lerdorf initially created these Personal Home Page Tools to replace a small set of Perl scripts he had been using to maintain his personal homepage. The tools were used to perform tasks such as displaying his résumé and recording how much traffic his page was receiving. He combined these binaries with his Form Interpreter to create PHP/FI, which had more functionality. PHP/FI included a larger implementation for the C programming language and could communicate with databases, enabling the building of simple, dynamic web applications. Lerdorf released PHP publicly on June 8, 1995 to accelerate bug location and improve the code. This release was named PHP version 2 and already had the basic functionality that PHP has today.

This included Perl-like variables, form handling, and the ability to embed HTML. The syntax was similar to Perl but was more limited, simpler, and less consistent.

Zeev Suraski and Andi Gutmans, two Israeli developers at the Technion IIT, rewrote the parser in 1997 and formed the base of PHP 3, changing the language's name to the recursive initialism PHP: Hypertext Preprocessor. The development team officially released PHP/FI 2 in November 1997 after months of beta testing. Afterwards, public testing of PHP 3 began, and the official launch came in June 1998. Suraski and Gutmans then started a new rewrite of PHP's core, producing the Zend Engine in 1999. They also founded Zend Technologies in Ramat Gan, Israel.

On May 22, 2000, PHP 4, powered by the Zend Engine 1.0, was released. On July 13, 2004, PHP 5 was released, powered by the new Zend Engine II. PHP 5 included new features such as improved support for object-oriented programming, the PHP Data Objects extension (which defines a lightweight and consistent interface for accessing databases), and numerous performance enhancements. The most recent update released by The PHP Group is for the older PHP version 4 code branch. As of August, 2008 this branch is up to version 4.4.9. PHP 4 is no longer under development nor will any security updates be released.

In 2008, PHP 5 became the only stable version under development. Late static binding has been missing from PHP and will be added in version 5.3. PHP 6 is under development alongside PHP 5. Major changes include the removal of register_globals,[14] magic quotes, and safe mode.The reason for the removals was because register_globals had given way to security holes, and magic quotes had an unpredictable nature, and was best avoided. Instead, to escape characters, Magic quotes may be substituted with the addslashes() function, or more appropriately an escape mechanism specific to the database vendor itself like mysql_real_escape_string() for MySQL.

PHP does not have complete native support for Unicode or multibyte strings;Unicode support will be included in PHP 6. Many high profile open source projects ceased to support PHP 4 in new code as of February 5, 2008, due to the GoPHP5 initiative, provided by a consortium of PHP developers promoting the transition from PHP 4 to PHP 5.

It runs in both 32-bit and 64-bit environments, but on Windows the only official distribution is 32-bit, requiring Windows 32-bit compatibility mode to be enabled while using IIS in a 64-bit Windows environment. There is a third-party distribution available for 64-bit Windows.

Release History

Meaning
Red	Old release; not supported
Yellow	Old release; still supported
Green	Current release
Blue	Future release

Major Version	Minor Version	Release date	Notes
1.0	1.0.0	1995-06-08	Officially called "Personal Home Page Tools (PHP Tools)". This is the first use of the name "PHP".
2.0	2.0.0	1996-04-16	Considered by its creator as the "fastest and simplest tool" for creating dynamic web pages.
3.0	3.0.0	1998-06-06	Development moves from one person to multiple developers. Zeev Suraski and Andi Gutmans rewrite the base for this version.
4.0	4.0.0	2000-05-22	Added more advanced two-stage parse/execute tag-parsing system called the Zend engine.
	4.1.0	2001-12-10	Introduced 'superglobals' (`$_GET`, `$_POST`, `$_SESSION`, etc.)
	4.2.0	2002-04-22	Disabled register_globals by default. Data received over the network is not inserted directly into the globalnamespace anymore, closing possible security holes in applications.
	4.3.0	2002-12-27	Introduced the CLI, in addition to the CGI.
	4.4.0	2005-07-11	Added man pages for `phpize` and `php-config` scripts.
	4.4.8	2008-01-03	Several security enhancements and bug fixes. Was to be the end of life release for PHP 4. Security updates only until 2008-08-08, if necessary.
	4.4.9	2008-08-07	More security enhancements and bug fixes. The last release of the PHP 4.4 series.
5.0	5.0.0	2004-07-13	Zend Engine II with a new object model.
	5.1.0	2005-11-24	Performance improvements with introduction of compiler variables in re-engineered PHP Engine.
	5.2.0	2006-11-02	Enabled the filter extension by default.
	5.2.8	2008-12-08^[26]	Emergent bug fix
	5.2.9	2009-02-26
	5.3.0	Second Quarter of 2009^[27]	Namespace support; Late static bindings, Jump label (limited goto), Closures, Native PHP archives (phar), Garbage collection, Persistent Connection with mysqli, sqlite3, Added fileinfo as a mime_magic replacement for better MIME support
6.0	6.0.0	No date set	Unicode support; removal of ereg extension, 'register_globals', 'magic_quotes' and 'safe_mode'; Alternative PHP Cache

Characteristics of PHP

Usage
Speed optimization
Security
Platform independent

Thus PHP had got succeeded in these days and even PHP is installed on more than 20 million websites and 1 million web servers.

Holographic Movie Storage

2009-03-19T05:39:00.000-07:00

Introduction

Holograms allow permanent optical data storage and retrieval with far higher densities than CDs or DVDs, using the interference patterns of two lasers. Physical chemists are now developing the technology into products based on optics that could store the equivalent of a movie on a thumb-sized hologram.

LONGMONT, Calif. -- The way we watch movies, television, listen to music, and store all kinds of data is changing. Soon it'll be possible to get everything you need or want saved on a disc no bigger than your thumb.

"So instead of having your movie on something the size of a standard disk, now you can talk about putting a movie on something maybe the size of a postage stamp -- if not smaller," Bill Wilson, chief scientist at InPhase Technologies in Longmont, Calif., tells DBIS.

Just think ... Your favorite movie or collection of songs stored on a single disc. Physical chemists say holograms are the holy grail of data storage.

Wilson says, "In many ways you can think of our disk as -- it's basically a library."

Two intersecting lasers store millions of bits of information on a disc. It's that intersection of those two beams that actually allows you to record the holographic data and later recover it.

It's the same concept as the images on credit cards we're all familiar with. Unlike the way information is stored on a CD, holographic storage stores information below the surface. And holographic storage promises to solve the movie industry's current "memory nightmare," thanks to optics. Right now all movies are stored on film because of its long shelf life. Even an epic like "Gone With the Wind," would take up only a tiny bit of holographic space.

"You know, Blockbuster could send out a disc with the top 50 movies of the month," Wilson says. The technology is here, now it's a question of how it will be used. "Well, that's a question for Warner Brothers."

InPhase Technologies and the Maxell company, known for VHS tapes, will start offering holographic storage systems for professionals late next year. The movie and broadcast industries will likely follow, but consumer products may take a while before they reach the marketplace.

Background

Scientists have developed a holographic data storage system that promises to revolutionize the way we store data. Movie and broadcast companies will be among the first users because the technology is well suited for broadcasting and video editing: data is read and stored in parallel at a million bits at a time, and prototypes of holographic disk arrays have data transfer rates of 27 megabytes per second. Eventually consumers will be able to purchase high-definition videos, and have greater storage capacity in their cell phones and digital cameras.

How It Works ?

While CDs and DVDs store information in single bits over the surface of the disk, holographic storage can store much more information faster (one million bits at a time) throughout the entire thickness of the disk. Holographic data storage would offer better copyright protection. DVDs and CDs can easily be copied by making an imprint of the "bumps" on the surface of the disk, but it's harder to this with holographic data storage because information is stored throughout the disks.

The key technology that makes this possible is the development of a material to make the disk that can support the way holograms are made. Earlier materials – most notably lithium niobate -- could be both recorded and read back, but in the process of reading back the data, the holograms were erased. Companies have been searching for the perfect recording material for 50 years. They haven't found it yet, but the emphasis has switched to polymeric materials onto which data can be recorded once, instead of being erasable.

About Holograms

A hologram records the interference pattern made by two beams of light that interact with each other. One beam comes directly from the laser, while the other comes from the same laser but bounces off the object being imaged. Light waves behave just like water waves when they meet. Wherever a crest of one coincides with a crest of the other, an extra high crest will form, and where two troughs coincide, they will form an extra low trough. If a crest meets a trough, the two will cancel each other out. With light, the waves will form light (crests) and dark (troughs) fringes -- the telltale wave pattern that can be recorded on photographic film. After it is developed, the hologram is lit by a beam of light to recreate the 3D object in space.

HTML and its History

2009-03-18T07:57:00.000-07:00

HTML, an initialism of HyperText Markup Language, is the predominant markup language for Web pages. It provides a means to describe the structure of text-based information in a document—by denoting certain text as links, headings, paragraphs, lists, and so on—and to supplement that text with interactive forms, embedded images, and other objects. HTML is written in the form of tags, surrounded by angle brackets. HTML can also describe, to some degree, the appearance and semantics of a document, and can include embedded scripting language code (such as JavaScript) which can affect the behavior of Web browsers and other HTML processors.

History of HTLM

Origins

In 1980, physicist Tim Berners-Lee, who was an independent contractor at CERN, proposed and prototyped ENQUIRE, a system for CERN researchers to use and share documents. In 1989, Berners-Lee and CERN data systems engineer Robert Cailliau each submitted separate proposals for an Internet-based hypertext system providing similar functionality. The following year, they collaborated on a joint proposal, the WorldWideWeb (W3) project, which was accepted by CERN.

First specifications

The first publicly available description of HTML was a document called HTML Tags, first mentioned on the Internet by Berners-Lee in late 1991. It describes 22 elements comprising the initial, relatively simple design of HTML. Thirteen of these elements still exist in HTML 4.

Berners-Lee considered HTML to be, at the time, an application of SGML, but it was not formally defined as such until the mid-1993 publication, by the IETF, of the first proposal for an HTML specification: Berners-Lee and Dan Connolly's "Hypertext Markup Language (HTML)" Internet-Draft, which included an SGML Document Type Definition to define the grammar.The draft expired after six months, but was notable for its acknowledgment of the NCSA Mosaic browser's custom tag for embedding in-line images, reflecting the IETF's philosophy of basing standards on successful prototypes.Similarly, Dave Raggett's competing Internet-Draft, "HTML+ (Hypertext Markup Format)", from late 1993, suggested standardizing already-implemented features like tables and fill-out forms.

After the HTML and HTML+ drafts expired in early 1994, the IETF created an HTML Working Group, which in 1995 completed "HTML 2.0", the first HTML specification intended to be treated as a standard against which future implementations should be based. Published as Request for Comments 1866, HTML 2.0 included ideas from the HTML and HTML+drafts .There was no "HTML 1.0"; the 2.0 designation was intended to distinguish the new edition from previous drafts.

Further development under the auspices of the IETF was stalled by competing interests. Since 1996, the HTML specifications have been maintained, with input from commercial software vendors, by the World Wide Web Consortium (W3C). However, in 2000, HTML also became an international standard (ISO/IEC 15445:2000). The last HTML specification published by the W3C is the HTML 4.01 Recommendation, published in late 1999. Its issues and errors were last acknowledged by errata published in 2001.

Version types in HTML

HTML has been developed extensively over the years:

1992
HTML is first defined
1993
HTML+ (some physical layout, fill-out forms, tables, math)
1994
HTML 2.0 (standard for core features)
HTML 3.0 (an extension of HTML+ submitted as a draft standard)
1995
Netscape-specific non-standard HTML appears
1996
Competing Netscape and Explorer versions of HTML
HTML 3.2 (standard based on current practices)
1997
HTML 4.0 (separates structure and presentation with stylesheets)
1999
HTML 4.01 (slight modifications only)
2000
XHTML 1.0 (XML version of HTML 4.01)
2001
XHTML 1.1 (modularization to allow different subsets)
2002
XHTML 2.0 (simplifying and generalizing several tags)

HTML markup

HTML markup consists of several key components, including elements (and their attributes), character-based data types, and character references and entity references. Another important component is the document type declaration, which specifies the Document Type Definition.[citation needed] As of HTML 5, no Document Type Definition will need to be specified, and will only determine the layout mode.

Delivery of HTML

HTML documents can be delivered by the same means as any other computer file; however, they are most often delivered either by HTTP from a Web server or by e-mail

HTTP

The World Wide Web is composed primarily of HTML documents transmitted from Web servers to Web browsers using the Hypertext Transfer Protocol (HTTP). However, HTTP is used to serve images, sound, and other content in addition to HTML. To allow the Web browser to know how to handle each document it receives, other information is transmitted along with the document. This metadata usually includes the MIME type (e.g. text/html or application/xhtml+xml) and the character encoding (see Character encodings in HTML).

In modern browsers, the MIME type that is sent with the HTML document may affect how the document is initially interpreted. A document sent with the XHTML MIME type is expected to be well-formed XML, and syntax errors may cause the browser to fail to render it. The same document sent with the HTML MIME type might be displayed successfully, since some browsers are more lenient with HTML.

The W3C recommendations state that XHTML 1.0 documents that follow guidelines set forth in the recommendation's Appendix C may be labeled with either MIME Type. The current XHTML 1.1 Working Draft also states that XHTML 1.1 documents should be labeled with either MIME type.

How to install Red hat linux 8--[ebook]

2009-03-18T02:24:00.000-07:00

Red hat Linux8 installation e book

[download]

C language and its history

2009-03-18T01:27:00.000-07:00

History

The initial development of C occurred at AT&T Bell Labs between 1969 and 1973; according to Ritchie, the most creative period occurred in 1972. It was named "C" because many of its features were derived from an earlier language called "B", which according to Ken Thompson was a stripped-down version of the BCPL programming language.

The origin of C is closely tied to the development of the Unix operating system, originally implemented in assembly language on a PDP-7 by Ritchie and Thompson, incorporating several ideas from colleagues. Eventually they decided to port the operating system to a PDP-11. B's lack of functionality to take advantage of some of the PDP-11's features, notably byte addressability, led to the development of an early version of the C programming language.

The original PDP-11 version of the Unix system was developed in assembly language. By 1973, with the addition of struct types, the
C language had become powerful enough that most of the Unix kernel was rewritten in C. This was one of the first operating system kernels implemented in a language other than assembly. (Earlier instances include the Multics system (written in PL/I), and MCP (Master Control Program) for the Burroughs B5000 written in ALGOL in 1961.)

What is c
C is a general-purpose computer programming language originally developed in 1972 by Dennis Ritchie at the Bell Telephone Laboratories to implement the Unix operating system.

Although C was designed for writing architecturally independent system software, it is also widely used for developing application software.

Worldwide, C is the first or second most popular language in terms of number of developer positions or publicly available code. It is widely used on many different software platforms, and there are few computer architectures for which a C compiler does not exist. C has greatly influenced many other popular programming languages, most notably C++, which originally began as an extension to C, and Java and C# which borrow C lexical conventions and operators.

Philosophy

C is an imperative (procedural) systems implementation language. It was designed to be compiled using a relatively straightforward compiler, to provide low-level access to memory, to provide language constructs that map efficiently to machine instructions, and to require minimal run-time support. C was therefore useful for many applications that had formerly been coded in assembly language.

Despite its low-level capabilities, the language was designed to encourage machine-independent programming. A standards-compliant and portably written C program can be compiled for a very wide variety of computer platforms and operating systems with little or no change to its source code, while approaching highest performance. The language has become available on a very wide range of platforms, from embedded microcontrollers to supercomputers.

Minimalism

C is designed to provide high-level abstracts for all the native features of a general-purpose CPU, while at the same time allowing modularization, structure, and code re-use. Features specific to a particular program's function (features that are not general to all platforms) are not included in the language or library definitions. However any such specific functions are implementable and accessible as external reusable libraries, in order to encourage module dissemination and re-use. C is somewhat strongly typed (emitting warnings or errors) but allows programmers to override types in the interests of flexibility, simplicity or performance; while being natural and well-defined in its interpretation of type overrides.

C's design is tied to its intended use as a portable systems implementation language. Consequently, it does not require run-time checks for conditions that would never occur in correct programs, it provides simple, direct access to any addressable object (for example, memory-mapped device control registers), and its source-code expressions can be translated in a straightforward manner to primitive machine operations in the executable code. Some early C compilers were comfortably implemented (as a few distinct passes communicating via intermediate files) on PDP-11 processors having only 16 address bits; however, C99 assumes a 512 KB minimum compilation platform.

Characteristics

Like most imperative languages in the ALGOL tradition, C has facilities for structured programming and allows lexical variable scope and recursion, while a static type system prevents many unintended operations. In C, all executable code is contained within functions. Function parameters are always passed by value. Pass-by-reference is achieved in C by explicitly passing pointer values. Heterogeneous aggregate data types (struct) allow related data elements to be combined and manipulated as a unit. C program source text is free-format, using the semicolon as a statement terminator (not a delimiter).

C also exhibits the following more specific characteristics:

* non-nestable function definitions
* variables may be hidden in nested blocks
* partially weak typing; for instance, characters can be used as integers
* low-level access to computer memory by converting machine addresses to typed pointers
* function and data pointers supporting ad hoc run-time polymorphism
* array indexing as a secondary notion, defined in terms of pointer arithmetic
* a preprocessor for macro definition, source code file inclusion, and conditional compilation
* complex functionality such as I/O, string manipulation, and mathematical functions consistently delegated to library routines
* A relatively small set of reserved keywords (originally 32, now 37 in C99)
* A lexical structure that resembles B more than ALGOL, for example
1.) { ... } rather than ALGOL's begin ... end
2.) the equal-sign is for assignment (copying), much like Fortran
3.) two consecutive equal-signs are to test for equality (compare to .EQ. in Fortran or the equal-sign in BASIC)
4.) && and || in place of ALGOL's and and or (these are semantically distinct from the bit-wise operators & and | because they will never evaluate the right operand if the result can be determined from the left alone (short-circuit evaluation)).
5.) a large number of compound operators, such as +=, ++, ......

Absent features

The relatively low-level nature of the language affords the programmer close control over what the computer does, while allowing special tailoring and aggressive optimization for a particular platform. This allows the code to run efficiently on very limited hardware, such as embedded systems.

C does not have some features that are available in some other programming languages:

* No assignment of arrays or strings (copying can be done via standard functions; assignment of objects having struct or union type is supported)
* No automatic garbage collection
* No requirement for bounds checking of arrays
* No operations on whole arrays
* No syntax for ranges, such as the A..B notation used in several languages
* No separate Boolean type: zero/nonzero is used instead
* No formal closures or functions as parameters (only function and variable pointers)
* No generators or coroutines; intra-thread control flow consists of nested function calls, except for the use of the longjmp or setcontext library functions
* No exception handling; standard library functions signify error conditions with the global errno variable and/or special return values
* Only rudimentary support for modular programming
* No compile-time polymorphism in the form of function or operator overloading
* Only rudimentary support for generic programming
* Very limited support for object-oriented programming with regard to polymorphism and inheritance
* Limited support for encapsulation
* No native support for multithreading and networking
* No standard libraries for computer graphics and several other application programming needs

A number of these features are available as extensions in some compilers, or can be supplied by third-party libraries, or can be simulated by adopting certain coding disciplines.

Uses

C's primary use is for "system programming", including implementing operating systems and embedded system applications, due to a combination of desirable characteristics such as code portability and efficiency, ability to access specific hardware addresses, ability to "pun" types to match externally imposed data access requirements, and low runtime demand on system resources.

One consequence of C's wide acceptance and efficiency is that C is used for other programs that are not directly used by end-users (compilers, libraries, interpreters, etc).

C is sometimes used as an intermediate language by implementations of other languages. This approach may be used for convenience (by using C as an intermediate language, it is not necessary to develop machine-specific code generators; ). Some compilers which use C this way are BitCC, Gambit, the Glasgow Haskell Compiler, Squeak, and valac.

Unfortunately, C was designed as a programming language, not as a compiler target language, and is thus less than ideal for use as an intermediate language. This has led to development of C-based intermediate languages such as C--.

C has also been widely used to implement end-user applications. Although as applications became larger, much of that development shifted to other languages.

Example program

The "hello, world" example which appeared in the first edition of K&R has become the model for an introductory program in most programming textbooks, regardless of programming language. The program prints "hello, world" to the standard output, which is usually a terminal or screen display. A standard-conforming "hello, world" program is

#include

int main(void)
{
printf("hello, world\n");
return 0;
}

How CD burners works

2009-03-17T09:34:00.000-07:00

Burning CDs: Laser Assembly

In the last section, we saw that CD burners darken microscopic areas of CD-R discs to record a digital pattern of reflective and non-reflective areas that can be read by a standard CD player. Since the data must be accurately encoded on such a small scale, the burning system must be extremely precise. Still, the basic process at work is quite simple.
The CD burner has a moving laser assembly, just like an ordinary CD player. But in addition to the standard "read laser," it has a "write laser." The write laser is more powerful than the read laser, so it interacts with the disc differently: It alters the surface instead of just bouncing light off it. Read lasers are not intense enough to darken the dye material, so simply playing a CD-R in a CD drive will not destroy any encoded information.

The laser assembly inside a CD burner

Burning CDs: Write Laser

The write laser moves in exactly the same way as the read laser: It moves outward while the disc spins. The bottom plastic layer has grooves pre-pressed into it, to guide the laser along the correct path. By calibrating the rate of spin with the movement of the laser assembly, the burner keeps the laser running along the track at a constant rate of speed. To record the data, the burner simply turns the laser writer on and off in synch with the pattern of 1s and 0s. The laser darkens the material to encode a 0 and leaves it translucent to encode a 1.
Most CD burners can create CDs at multiple speeds. At 1x speed, the CD spins at about the same rate as it does when the player is reading it. This means it would take you about 60 minutes to record 60 minutes of music. At 2x speed, it would take you about half an hour to record 60 minutes, and so on. For faster burning speeds, you need more advanced laser-control systems and a faster connection between the computer and the burner. You also need a blank disc that is designed to record information at this speed.

A CD has a long, spiraled data track.
If you were to unwind this track,
would extend out 3.5 miles (5 km)

The main advantage of CD-R discs is that they work in almost all CD players and CD-ROMS, which are among the most prevalent media players today. In addition to this wide compatibility, CD-Rs are relatively inexpensive.

The machinery in a CD burner looks pretty much the same as the machinery in any CD player.
There is a mechanism that spins the disc and another mechanism that slides the laser assembly.

The main drawback of the format is that you can't reuse the discs. Once you've burned in the digital pattern, it can't be erased and re-written. In the mid '90s, electronics manufacturers introduced a new CD format that addressed this problem. In the next section, we'll look at these CD-rewritable discs, commonly called CD-RWs, to see how they differ from standard CD-R discs.

Erasing CDs

In the last section, we looked at the most prevalent writable CD technology, CD-R. CD-R discs hold a lot of data, work with most CD players and are fairly inexpensive. But unlike tapes, floppy disks and many other data-storage mediums, you cannot re-record on CD-R disc once you've filled it up.

CD-RW discs have taken the idea of writable CDs a step further, building in an erase function so you can record over old data you don't need anymore. These discs are based on phase-change technology. In CD-RW discs, the phase-change element is a chemical compound of silver, antimony, tellurium and indium. As with any physical material, you can change this compound's form by heating it to certain temperatures. When the compound is heated above its melting temperature (around 600 degrees Celsius), it becomes a liquid; at its crystallization temperature (around 200 degrees Celsius), it turns into a solid.

In a CD-RW disc, the reflecting lands and non-reflecting bumps of a conventional CD are represented by phase shifts in a special compound. When the compound is in a crystalline state, it is translucent, so light can shine through to the metal layer above and reflect back to the laser assembly. When the compound is melted into an amorphous state, it becomes opaque, making the area non-reflective.

Phase-change Compounds

In phase-change compounds, these shifts in form can be "locked into place": They persist even after the material cools down again. If you heat the compound in CD-RW discs to the melting temperature and let it cool rapidly, it will remain in a fluid, amorphous state, even though it is below the crystallization temperature. In order to crystallize the compound, you have to keep it at the crystallization temperature for a certain length of time so that it turns into a solid before it cools down again.

In the compound used in CD-RW discs, the crystalline form is translucent while the amorphous fluid form will absorb most light. On a new, blank CD, all of the material in the writable area is in the crystalline form, so light will shine through this layer to the reflective metal above and bounce back to the light sensor. To encode information on the disc, the CD burner uses its write laser, which is powerful enough to heat the compound to its melting temperature. These "melted" spots serve the same purpose as the bumps on a conventional CD and the opaque spots on a CD-R: They block the "read" laser so it won't reflect off the metal layer. Each non-reflective area indicates a 0 in the digital code. Every spot that remains crystalline is still reflective, indicating a 1.

The Erase Laser

As with CD-Rs, the read laser does not have enough power to change the state of the material in the recording layer -- it's a lot weaker than the write laser. The erase laser falls somewhere in between: While it isn't strong enough to melt the material, it does have the necessary intensity to heat the material to the crystallization point. By holding the material at this temperature, the erase laser restores the compound to its crystalline state, effectively erasing the encoded 0. This clears the disc so new data can be encoded.

CD-RW discs do not reflect as much light as older CD formats, so they cannot be read by most older CD players and CD-ROM drives. Some newer drives and players, including all CD-RW writers, can adjust the read laser to work with different CD formats. But since CD-RWs will not work on many CD players, these are not a good choice for music CDs. For the most part, they are used as back-up storage devices for computer files.

As we've seen, the reflective and non-reflective patterns on a CD are incredibly small, and they are burned and read very quickly with a speeding laser beam. In this system, the chances of a data error are fairly high. In the next section, we'll look at some of the ways that CD burners compensate for various encoding problems.

Fingerprint Scanners(Biometrics)

2009-03-17T05:57:00.000-07:00

Introduction

Computerized fingerprint scanners have been a mainstay of spy thrillers for decades, but up until recently, they were pretty exotic technology in the real world. In the past few years, however, scanners have started popping up all over the place -- in police stations, high-security buildings and even on PC keyboards. You can pick up a personal USB fingerprint scanner for less than $100, and just like that, your computer's guarded by high-tech biometrics. Instead of, or in addition to, a password, you need your distinctive print to gain access.

How it Works ?

Basics

Fingerprints are one of those bizarre twists of nature. Human beings happen to have built-in, easily accessible identity cards. You have a unique design, which represents you alone, literally at your fingertips. How did this happen?
People have tiny ridges of skin on their fingers because this particular adaptation was extremely advantageous to the ancestors of the human species. The pattern of ridges and "valleys" on fingers make it easier for the hands to grip things, in the same way a rubber tread pattern helps a tire grip the road.

The other function of fingerprints is a total coincidence. Like everything in the human body, these ridges form through a combination of genetic and environmental factors. The genetic code in DNA gives general orders on the way skin should form in a developing fetus, but the specific way it forms is a result of random events. The exact position of the fetus in the womb at a particular moment and the exact composition and density of surrounding amniotic fluid decides how every individual ridge will form.

So, in addition to the countless things that go into deciding your genetic make-up in the first place, there are innumerable environmental factors influencing the formation of the fingers. Just like the weather conditions that form clouds or the coastline of a beach, the entire development process is so chaotic that, in the entire course of human history, there is virtually no chance of the same exact pattern forming twice.

Consequently, fingerprints are a unique marker for a person, even an identical twin. And while two prints may look basically the same at a glance, a trained investigator or an advanced piece of software can pick out clear, defined differences.

This is the basic idea of fingerprint analysis, in both crime investigation and security. A fingerprint scanner's job is to take the place of a human analyst by collecting a print sample and comparing it to other samples on record.

A fingerprint scanner system has two basic jobs -- it needs to get an image of your finger, and it needs to determine whether the pattern of ridges and valleys in this image matches the pattern of ridges and valleys in pre-scanned images.

There are a number of different ways to get an image of somebody's finger. The most common methods today are optical scanning and capacitance scanning.

Optical Scanner

The heart of an optical scanner is a charge coupled device (CCD), the same light sensor system used in digital cameras and camcorders. A CCD is simply an array of light-sensitive diodes called photosites, which generate an electrical signal in response to light photons. Each photosite records a pixel, a tiny dot representing the light that hit that spot. Collectively, the light and dark pixels form an image of the scanned scene (a finger, for example). Typically, an analog-to-digital converter in the scanner system processes the analog electrical signal to generate a digital representation of this image.

The scanning process starts when you place your finger on a glass plate, and a CCD camera takes a picture. The scanner has its own light source, typically an array of light-emitting diodes, to illuminate the ridges of the finger. The CCD system actually generates an inverted image of the finger, with darker areas representing more reflected light (the ridges of the finger) and lighter areas representing less reflected light (the valleys between the ridges).

Before comparing the print to stored data, the scanner processor makes sure the CCD has captured a clear image. It checks the average pixel darkness, or the overall values in a small sample, and rejects the scan if the overall image is too dark or too light. If the image is rejected, the scanner adjusts the exposure time to let in more or less light, and then tries the scan again.

If the darkness level is adequate, the scanner system goes on to check the image definition (how sharp the fingerprint scan is). The processor looks at several straight lines moving horizontally and vertically across the image. If the fingerprint image has good definition, a line running perpendicular to the ridges will be made up of alternating sections of very dark pixels and very light pixels.

If the processor finds that the image is crisp and properly exposed, it proceeds to comparing the captured fingerprint with fingerprints on file.

Capacitance Scanner

Like optical scanners, capacitive fingerprint scanners generate an image of the ridges and valleys that make up a fingerprint. But instead of sensing the print using light, the capacitors use electrical current.

The diagram below shows a simple capacitive sensor. The sensor is made up of one or more semiconductor chips an array of tiny cells. Each cell includes two conductor plates, covered with an insulating layer. The cells are tiny -- smaller than the width of one ridge on a finger.

The sensor is connected to an integrator, an electrical circuit built around an inverting operational amplifier. The inverting amplifier is a complex semiconductor device, made up of a number of transistors, resistors and capacitors. The details of its operation would fill an entire article by itself, but here we can get a general sense of what it does in a capacitance scanner. (Check out this page on operational amplifiers for a technical overview.)

Like any amplifier, an inverting amplifier alters one current based on fluctuations in another current. Specifically, the inverting amplifier alters a supply voltage. The alteration is based on the relative voltage of two inputs, called the inverting terminal and the non-inverting terminal. In this case, the non-inverting terminal is connected to ground, and the inverting terminal is connected to a reference voltage supply and a feedback loop. The feedback loop, which is also connected to the amplifier output, includes the two conductor plates.

As you may have recognized, the two conductor plates form a basic capacitor, an electrical component that can store up charge. The surface of the finger acts as a third capacitor plate, separated by the insulating layers in the cell structure and, in the case of the fingerprint valleys, a pocket of air. Varying the distance between the capacitor plates (by moving the finger closer or farther away from the conducting plates) changes the total capacitance (ability to store charge) of the capacitor. Because of this quality, the capacitor in a cell under a ridge will have a greater capacitance than the capacitor in a cell under a valley.

To scan the finger, the processor first closes the reset switch for each cell, which shorts each amplifier's input and output to "balance" the integrator circuit. When the switch is opened again, and the processor applies a fixed charge to the integrator circuit, the capacitors charge up. The capacitance of the feedback loop's capacitor affects the voltage at the amplifier's input, which affects the amplifier's output. Since the distance to the finger alters capacitance, a finger ridge will result in a different voltage output than a finger valley.

The scanner processor reads this voltage output and determines whether it is characteristic of a ridge or a valley. By reading every cell in the sensor array, the processor can put together an overall picture of the fingerprint, similar to the image captured by an optical scanner.

The main advantage of a capacitive scanner is that it requires a real fingerprint-type shape, rather than the pattern of light and dark that makes up the visual impression of a fingerprint. This makes the system harder to trick. Additionally, since they use a semiconductor chip rather than a CCD unit, capacitive scanners tend to be more compact that optical devices.

Analysis

most fingerprint scanner systems compare specific features of the fingerprint, generally known as minutiae. Typically, human and computer investigators concentrate on points where ridge lines end or where one ridge splits into two (bifurcations). Collectively, these and other distinctive features are sometimes called typica.

The scanner system software uses highly complex algorithms to recognize and analyze these minutiae. The basic idea is to measure the relative positions of minutiae, in the same sort of way you might recognize a part of the sky by the relative positions of stars. A simple way to think of it is to consider the shapes that various minutia form when you draw straight lines between them. If two prints have three ridge endings and two bifurcations, forming the same shape with the same dimensions, there's a high likelihood they're from the same print.

To get a match, the scanner system doesn't have to find the entire pattern of minutiae both in the sample and in the print on record, it simply has to find a sufficient number of minutiae patterns that the two prints have in common. The exact number varies according to the scanner programming.

About Scanners

2009-03-16T07:47:00.000-07:00

Introduction:

Scanners have become an important part of the home office over the last few years. Scanner technology is everywhere and used in many ways:.

The basic principle of a scanner is to analyze an image and process it in some way. Image and text capture (optical character recognition or OCR) allow you to save information to a file on your computer. You can then alter or enhance the image, print it out or use it on your Web page.

The different types of scanners are :

Flatbed scanners, also called desktop scanners, are the most versatile and commonly used scanners.

Sheet-fed scanners are similar to flatbed scanners except the document is moved and the scan head is immobile. A sheet-fed scanner looks a lot like a small portable printer.

Handheld scanners use the same basic technology as a flatbed scanner, but rely on the user to move them instead of a motorized belt. This type of scanner typically does not provide good image quality. However, it can be useful for quickly capturing text.

Drum scanners are used by the publishing industry to capture incredibly detailed images. They use a technology called a photomultiplier tube (PMT). In PMT, the document to be scanned is mounted on a glass cylinder. At the center of the cylinder is a sensor that splits light bounced from the document into three beams. Each beam is sent through a color filter into a photomultiplier tube where the light is changed into an electrical signal.

Structure of a scanner:

Parts of a typical flatbed scanner include:

Charge-coupled device (CCD) array
Mirrors
Scan head
Glass plate
Lamp
Lens
Cover
Filters
Stepper motor
Stabilizer bar
Belt
Power supply
Interface port(s)
Control circuitry

The core component of the scanner is the CCD array. CCD is the most common technology for image capture in scanners. CCD is a collection of tiny light-sensitive diodes, which convert photons (light) into electrons (electrical charge). These diodes are called photosites. In a nutshell, each photosite is sensitive to light -- the brighter the light that hits a single photosite, the greater the electrical charge that will accumulate at that site.

Photons hitting a photosite and creating electrons
The image of the document that you scan reaches the CCD array through a series of mirrors, filters and lenses. The exact configuration of these components will depend on the model of scanner, but the basics are pretty much the same.

The Scanning process:

Here are the steps that a scanner goes through when it scans a document:

The document is placed on the glass plate and the cover is closed. The inside of the cover in most scanners is flat white, although a few are black. The cover provides a uniform background that the scanner software can use as a reference point for determining the size of the document being scanned. Most flatbed scanners allow the cover to be removed for scanning a bulky object, such as a page in a thick book.

In the image above, you can see the fluorescent lamp on top of the scan head.

A lamp is used to illuminate the document. The lamp in newer scanners is either a cold cathode fluorescent lamp (CCFL) or a xenon lamp, while older scanners may have a standard fluorescent lamp.
The entire mechanism (mirrors, lens, filter and CCD array) make up the scan head. The scan head is moved slowly across the document by a belt that is attached to a stepper motor. The scan head is attached to a stabilizer bar to ensure that there is no wobble or deviation in the pass. Pass means that the scan head has completed a single complete scan of the document.

The stabilizer bar is very durable and tightly secured to the body of the scanner.

The image of the document is reflected by an angled mirror to another mirror. In some scanners, there are only two mirrors while others use a three mirror approach. Each mirror is slightly curved to focus the image it reflects onto a smaller surface.
The last mirror reflects the image onto a lens. The lens focuses the image through a filter on the CCD array.

Look carefully at the image above and you can see all three of the mirrors plus the lens assembly in this scan head.

The filter and lens arrangement vary based on the scanner. Some scanners use a three pass scanning method. Each pass uses a different color filter (red, green or blue) between the lens and CCD array. After the three passes are completed, the scanner software assembles the three filtered images into a single full-color image.

Click on the green Scan button to see the scanning process.

Most scanners today use the single pass method. The lens splits the image into three smaller versions of the original. Each smaller version passes through a color filter (either red, green or blue) onto a discrete section of the CCD array. The scanner combines the data from the three parts of the CCD array into a single full-color image.

Another imaging array technology that has become popular in inexpensive flatbed scanners is contact image sensor (CIS). CIS replaces the CCD array, mirrors, filters, lamp and lens with rows of red, green and blue light emitting diodes (LEDs). The image sensor mechanism, consisting of 300 to 600 sensors spanning the width of the scan area, is placed very close to the glass plate that the document rests upon. When the image is scanned, the LEDs combine to provide white light. The illuminated image is then captured by the row of sensors. CIS scanners are cheaper, lighter and thinner, but do not provide the same level of quality and resolution found in most CCD scanners.

Resolution and Interpolation:

Scanners vary in resolution and sharpness. Most flatbed scanners have a true hardware resolution of at least 300x300 dots per inch (dpi). The scanner's dpi is determined by the number of sensors in a single row (x-direction sampling rate) of the CCD or CIS array by the precision of the stepper motor (y-direction sampling rate).

The precision of the stepper motor determines the y-direction sampling rate.

For example, if the resolution is 300x300 dpi and the scanner is capable of scanning a letter-sized document, then the CCD has 2,550 sensors arranged in each horizontal row. A single-pass scanner would have three of these rows for a total of 7,650 sensors. The stepper motor in our example is able to move in increments equal to 1/300ths of an inch. Likewise, a scanner with a resolution of 600x300 has a CCD array with 5,100 sensors in each horizontal row.

Most scanners have a scan area that is either letter size (8.5x11 inches, 21.6x27.9 centimeters) or legal size (11x14 inches, 27.9x35.6 centimeters).

Sharpness depends mainly on the quality of the optics used to make the lens and the brightness of the light source. A bright xenon lamp and high-quality lens will create a much clearer, and therefore sharper, image than a standard fluorescent lamp and basic lens.

Of course, many scanners proclaim resolutions of 4,800x4,800 or even 9,600x9,600. To achieve a hardware resolution with a x-direction sampling rate of 9,600 would require a CCD array of 81,600 sensors. If you look at the specifications, these high resolutions are usually labeled software-enhanced, interpolated resolution or something similar. What does that mean?

Interpolation is a process that the scanning software uses to increase the perceived resolution of an image. It does this by creating extra pixels in between the ones actually scanned by the CCD array. These extra pixels are an average of the adjacent pixels. For example, if the hardware resolution is 300x300 and the interpolated resolution is 600x300, then the software is adding a pixel between every one scanned by a CCD sensor in each row.

Another term used when talking about scanners is bit depth, also called color depth. This simply refers to the number of colors that the scanner is capable of reproducing. Each pixel requires 24 bits to create standard true color and virtually all scanners on the market support this. Many of them offer bit depths of 30 or 36 bits. They still only output in 24-bit color, but perform internal processing to select the best possible choice out of the colors available in the increased palette. There are many opinions about whether there is a noticeable difference in quality between 24-, 30- and 36-bit scanners.

Image transfer:

Scanning the document is only one part of the process. For the scanned image to be useful, it must be transferred to your computer. There are three common connections used by scanners:

Parallel - Connecting through the parallel port is the slowest transfer method available.
Small Computer System Interface (SCSI) - SCSI requires a special SCSI connection. Most SCSI scanners include a dedicated SCSI card to insert into your computer and connect the scanner to, but you can use a standard SCSI controller instead.
Universal Serial Bus (USB) - USB scanners combine good speed, ease of use and affordability in a single package.
FireWire - Usually found on higher-end scanners,FireWire connections are faster than USB and SCSI. FireWire is ideal for scanning high-resolution images.

A scanner may have more than one way of connecting
to your computer.

On your computer, you need software, called a driver, that knows how to communicate with the scanner. Most scanners speak a common language, TWAIN. The TWAIN driver acts as an interpreter between any application that supports the TWAIN standard and the scanner. This means that the application does not need to know the specific details of the scanner in order to access it directly. For example, you can choose to acquire an image from the scanner from within Adobe Photoshop because Photoshop supports the TWAIN standard.

In addition to the driver, most scanners come with other software. Typically, a scanning utility and some type of image editing application are included. A lot of scanners include OCR software. OCR allows you to scan in words from a document and convert them into computer-based text. It uses an averaging process to determine what the shape of a character is and match it to the correct letter or number.

The great thing about scanner technology today is that you can get exactly what you need. You can find a decent scanner with good software for less than $200, or get a fantastic scanner with incredible software for less than $1,000. It all depends on your needs and budget.

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2009-03-16T07:21:00.000-07:00

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2009-03-15T09:48:00.000-07:00

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About Firewall

2009-03-14T15:07:00.001-07:00

Introduction:

If you have been using the Internet for any length of time, and especially if you work at a larger company and browse the Web while you are at work, you have probably heard the term firewall used. For example, you often hear people in companies say things like, "I can't use that site because they won't let it through the firewall."

If you have a fast Internet connection into your home (either a DSL connection or a cable modem), you may have found yourself hearing about firewalls for your home network as well. It turns out that a small home network has many of the same security issues that a large corporate network does. You can use a firewall to protect your home network and family from offensive Web sites and potential hackers.

Basically, a firewall is a barrier to keep destructive forces away from your property. In fact, that's why its called a firewall. Its job is similar to a physical firewall that keeps a fire from spreading from one area to the next.

What it does?

A firewall is simply a program or hardware device that filters the information coming through the Internet connection into your private network or computer system. If an incoming packet of information is flagged by the filters, it is not allowed through.

Let's say that you work at a company with 500 employees.The company will therefore have hundreds of computers that all have network cards connecting them together. In addition, the company will have one or more connections to the Internet through something like T1 or T3 lines. Without a firewall in place, all of those hundreds of computers are directly accessible to anyone on the Internet. A person who knows what he or she is doing can probe those computers, try to make FTP connections to them, try to make telnet connections to them and so on. If one employee makes a mistake and leaves a security hole, hackers can get to the machine and exploit the hole.

With a firewall in place, the landscape is much different. A company will place a firewall at every connection to the Internet (for example, at every T1 line coming into the company). The firewall can implement security rules. For example, one of the security rules inside the company might be:

Out of the 500 computers inside this company, only one of them is permitted to receive public FTP traffic. Allow FTP connections only to that one computer and prevent them on all others. A company can set up rules like this for FTP servers, Web servers, Telnet servers and so on. In addition, the company can control how employees connect to Web sites, whether files are allowed to leave the company over the network and so on. A firewall gives a company tremendous control over how people use the network.

Firewalls use one or more of three methods to control traffic flowing in and out of the network:

Packet filtering - Packets (small chunks of data) are analyzed against a set of filters. Packets that make it through the filters are sent to the requesting system and all others are discarded.

Proxy service - Information from the Internet is retrieved by the firewall and then sent to the requesting system and vice versa.

Stateful inspection - A newer method that doesn't examine the contents of each packet but instead compares certain key parts of the packet to a database of trusted information. Information traveling from inside the firewall to the outside is monitored for specific defining characteristics, then incoming information is compared to these characteristics. If the comparison yields a reasonable match, the information is allowed through. Otherwise it is discarded.

Firewall Configuration:

Firewalls are customizable. This means that you can add or remove filters based on several conditions. Some of these are:

IP addresses - Each machine on the Internet is assigned a unique address called an IP address. IP addresses are 32-bit numbers, normally expressed as four "octets" in a "dotted decimal number." A typical IP address looks like this: 216.27.61.137. For example, if a certain IP address outside the company is reading too many files from a server, the firewall can block all traffic to or from that IP address.

Domain names - Because it is hard to remember the string of numbers that make up an IP address, and because IP addresses sometimes need to change, all servers on the Internet also have human-readable names, called domain names. For example, it is easier for most of us to remember www.infoguyz.co.nr than it is to remember 216.27.61.137. A company might block all access to certain domain names, or allow access only to specific domain names.

Protocols - The protocol is the pre-defined way that someone who wants to use a service talks with that service. The "someone" could be a person, but more often it is a computer program like a Web browser. Protocols are often text, and simply describe how the client and server will have their conversation. The http in the Web's protocol. Some common protocols that you can set firewall filters for include IP, TCP, etc...,

Specific words and phrases - This can be anything. The firewall will sniff (search through) each packet of information for an exact match of the text listed in the filter. For example, you could instruct the firewall to block any packet with the word "X-rated" in it. The key here is that it has to be an exact match. The "X-rated" filter would not catch "X rated" (no hyphen). But you can include as many words, phrases and variations of them as you need.

Some operating systems come with a firewall built in. Otherwise, a software firewall can be installed on the computer in your home that has an Internet connection. This computer is considered a gateway because it provides the only point of access between your home network and the Internet.

Why it need?

There are many creative ways that unscrupulous people use to access or abuse unprotected computers:

Remote login - When someone is able to connect to your computer and control it in some form. This can range from being able to view or access your files to actually running programs on your computer.
Application backdoors - Some programs have special features that allow for remote access. Others contain bugs that provide a backdoor, or hidden access, that provides some level of control of the program.
SMTP session hijacking - SMTP is the most common method of sending e-mail over the Internet. By gaining access to a list of e-mail addresses, a person can send unsolicited junk e-mail (spam) to thousands of users. This is done quite often by redirecting the e-mail through the SMTP server of an unsuspecting host, making the actual sender of the spam difficult to trace.
Operating system bugs - Like applications, some operating systems have backdoors. Others provide remote access with insufficient security controls or have bugs that an experienced hacker can take advantage of.
Denial of service - You have probably heard this phrase used in news reports on the attacks on major Web sites. This type of attack is nearly impossible to counter. What happens is that the hacker sends a request to the server to connect to it. When the server responds with an acknowledgement and tries to establish a session, it cannot find the system that made the request. By inundating a server with these unanswerable session requests, a hacker causes the server to slow to a crawl or eventually crash.
E-mail bombs - An e-mail bomb is usually a personal attack. Someone sends you the same e-mail hundreds or thousands of times until your e-mail system cannot accept any more messages.
Macros - To simplify complicated procedures, many applications allow you to create a script of commands that the application can run. This script is known as a macro. Hackers have taken advantage of this to create their own macros that, depending on the application, can destroy your data or crash your computer.
Viruses - Probably the most well-known threat is computer viruses. A virus is a small program that can copy itself to other computers. This way it can spread quickly from one system to the next. Viruses range from harmless messages to erasing all of your data.
Spam - Typically harmless but always annoying, spam is the electronic equivalent of junk mail. Spam can be dangerous though. Quite often it contains links to Web sites. Be careful of clicking on these because you may accidentally accept a cookie that provides a backdoor to your computer.
Redirect bombs - Hackers can use ICMP to change (redirect) the path information takes by sending it to a different router. This is one of the ways that a denial of service attack is set up.
Source routing - In most cases, the path a packet travels over the Internet (or any other network) is determined by the routers along that path. But the source providing the packet can arbitrarily specify the route that the packet should travel. Hackers sometimes take advantage of this to make information appear to come from a trusted source or even from inside the network! Most firewall products disable source routing by default.

Some of the items in the list above are hard, if not impossible, to filter using a firewall. While some firewalls offer virus protection, it is worth the investment to install anti-virus software on each computer. And, even though it is annoying, some spam is going to get through your firewall as long as you accept e-mail.

The level of security you establish will determine how many of these threats can be stopped by your firewall. The highest level of security would be to simply block everything. Obviously that defeats the purpose of having an Internet connection. But a common rule of thumb is to block everything, then begin to select what types of traffic you will allow. You can also restrict traffic that travels through the firewall so that only certain types of information, such as e-mail, can get through. This is a good rule for businesses that have an experienced network administrator that understands what the needs are and knows exactly what traffic to allow through. For most of us, it is probably better to work with the defaults provided by the firewall developer unless there is a specific reason to change it.

One of the best things about a firewall from a security standpoint is that it stops anyone on the outside from logging onto a computer in your private network. While this is a big deal for businesses, most home networks will probably not be threatened in this manner. Still, putting a firewall in place provides some peace of mind.

How Ethernet Works ??

2009-03-14T09:39:00.000-07:00

The Ethernet

In 1973, at Xerox Corporation’s Palo Alto Research Center (more commonly known as PARC), researcher Bob Metcalfe designed and tested the first Ethernet network. While working on a way to link Xerox’s "Alto" computer to a printer, Metcalfe developed the physical method of cabling that connected devices on the Ethernet as well as the standards that governed communication on the cable. Ethernet has since become the most popular and most widely deployed network technology in the world. Many of the issues involved with Ethernet are common to many network technologies, and understanding how Ethernet addressed these issues can provide a foundation that will improve your understanding of networking in general.

The Ethernet standard has grown to encompass new technologies as computer networking has matured, but the mechanics of operation for every Ethernet network today stem from Metcalfe’s original design. The original Ethernet described communi -cation over a single cable shared by all devices on the network. Once a device attached to this cable, it had the ability to communicate with any other attached device. This allows the network to expand to accommodate new devices without requiring any modification to those devices already on the network.

Connecting Ethernet Cable wire in to slot

Ethernet Basics

Ethernet is a local area technology, with networks traditionally operating within a single building, connecting devices in close proximity. At most, Ethernet devices could have only a few hundred meters of cable between them, making it impractical to connect geographically dispersed locations. Modern advancements have increased these distances considerably, allowing Ethernet networks to span tens of kilometers.

Protocols

In networking, the term protocol refers to a set of rules that govern communications. Protocols are to computers what language is to humans. Since this article is in English, to understand it you must be able to read English. Similarly, for two devices on a network to successfully communicate, they must both understand the same protocols.

Ethernet Terminology

Ethernet follows a simple set of rules that govern its basic operation. To better understand these rules, it is important to understand the basics of Ethernet terminology.

* Medium - Ethernet devices attach to a common medium that provides a path along which the electronic signals will travel. Historically, this medium has been coaxial copper cable, but today it is more commonly a twisted pair or fiber optic cabling.

* Segment - We refer to a single shared medium as an Ethernet segment.

* Node - Devices that attach to that segment are stations or nodes.

* Frame - The nodes communicate in short messages called frames, which are variably sized chunks of information.

Frames are analogous to sentences in human language. In English, we have rules for constructing our sentences:
We know that each sentence must contain a subject and a predicate. The Ethernet protocol specifies a set of rules for constructing frames. There are explicit minimum and maximum lengths for frames, and a set of required pieces of information that must appear in the frame. Each frame must include, for example, both a destination address and a source address, which identify the recipient and the sender of the message. The address uniquely identifies the node, just as a name identifies a particular person. No two Ethernet devices should ever have the same address.

Ethernet Medium

Since a signal on the Ethernet medium reaches every attached node, the destination address is critical to identify the intended recipient of the frame.

For example, in the figure above, when computer B transmits to printer C, computers A and D will still receive and examine the frame. However, when a station first receives a frame, it checks the destination address to see if the frame is intended for itself. If it is not, the station discards the frame without even examining its contents.

One interesting thing about Ethernet addressing is the implementation of a broadcast address. A frame with a destination address equal to the broadcast address (simply called a broadcast, for short) is intended for every node on the network, and every node will both receive and process this type of frame.

CSMA/CD

The acronym CSMA/CD signifies carrier-sense multiple access with collision detection and describes how the Ethernet protocol regulates communication among nodes. While the term may seem intimidating, if we break it apart into its component concepts we will see that it describes rules very similar to those that people use in polite conversation. To help illustrate the operation of Ethernet, we will use an analogy of a dinner table conversation.

Let’s represent our Ethernet segment as a dinner table, and let several people engaged in polite conversation at the table represent the nodes. The term multiple access covers what we already discussed above: When one Ethernet station transmits, all the stations on the medium hear the transmission, just as when one person at the table talks, everyone present is able to hear him or her.

Now let's imagine that you are at the table and you have something you would like to say. At the moment, however, I am talking. Since this is a polite conversation, rather than immediately speak up and interrupt, you would wait until I finished talking before making your statement. This is the same concept described in the Ethernet protocol as carrier sense. Before a station transmits, it "listens" to the medium to determine if another station is transmitting. If the medium is quiet, the station recognizes that this is an appropriate time to transmit.

Collision Detection

Carrier-sense multiple access gives us a good start in regulating our conversation, but there is one scenario we still need to address. Let’s go back to our dinner table analogy and imagine that there is a momentary lull in the conversation. You and I both have something we would like to add, and we both "sense the carrier" based on the silence, so we begin speaking at approximately the same time. In Ethernet terminology, a collision occurs when we both spoke at once.

In our conversation, we can handle this situation gracefully. We both hear the other speak at the same time we are speaking, so we can stop to give the other person a chance to go on. Ethernet nodes also listen to the medium while they transmit to ensure that they are the only station transmitting at that time. If the stations hear their own transmission returning in a garbled form, as would happen if some other station had begun to transmit its own message at the same time, then they know that a collision occurred. A single Ethernet segment is sometimes called a collision domain because no two stations on the segment can transmit at the same time without causing a collision. When stations detect a collision, they cease transmission, wait a random amount of time, and attempt to transmit when they again detect silence on the medium.

The random pause and retry is an important part of the protocol. If two stations collide when transmitting once, then both will need to transmit again. At the next appropriate chance to transmit, both stations involved with the previous collision will have data ready to transmit. If they transmitted again at the first opportunity, they would most likely collide again and again indefinitely. Instead, the random delay makes it unlikely that any two stations will collide more than a few times in a row.

Limitations of Ethernet

A single shared cable can serve as the basis for a complete Ethernet network, which is what we discussed above. However, there are practical limits to the size of our Ethernet network in this case. A primary concern is the length of the shared cable.

Electrical signals propagate along a cable very quickly, but they weaken as they travel, and electrical interference from neighboring devices (fluorescent lights, for example) can scramble the signal. A network cable must be short enough that devices at opposite ends can receive each other's signals clearly and with minimal delay. This places a distance limitation on the maximum separation between two devices (called the network diameter) on an Ethernet network. Additionally, since in CSMA/CD only a single device can transmit at a given time, there are practical limits to the number of devices that can coexist in a single network. Attach too many devices to one shared segment and contention for the medium will increase. Every device may have to wait an inordinately long time before getting a chance to transmit.

Engineers have developed a number of network devices that alleviate these difficulties. Many of these devices are not specific to Ethernet, but play roles in other network technologies as well.

Repeaters

The first popular Ethernet medium was a copper coaxial cable known as "thicknet." The maximum length of a thicknet cable was 500 meters. In large building or campus environments, a 500-meter cable could not always reach every network device. A repeater addresses this problem.

Repeaters connect multiple Ethernet segments, listening to each segment and repeating the signal heard on one segment onto every other segment connected to the repeater. By running multiple cables and joining them with repeaters, you can significantly increase your network diameter.

Segmentation

In our dinner table analogy, we had only a few people at a table carrying out the conversation, so restricting ourselves to a single speaker at any given time was not a significant barrier to communication. But what if there were many people at the table and only one were allowed to speak at any given time?

In practice, we know that the analogy breaks down in circumstances such as these. With larger groups of people, it is common for several different conversations to occur simultaneously. If only one person in a crowded room or at a banquet dinner were able to speak at any time, many people would get frustrated waiting for a chance to talk. For humans, the problem is self-correcting: Voices only carry so far, and the ear is adept at picking out a particular conversation from the surrounding noise. This makes it easy for us to have many small groups at a party converse in the same room; but network cables carry signals quickly and efficiently over long distances, so this natural segregation of conversations does not occur.

Ethernet networks faced congestion problems as they increased in size. If a large number of stations connected to the same segment and each generated a sizable amount of traffic, many stations may attempt to transmit whenever there was an opportunity. Under these circumstances, collisions would become more frequent and could begin to choke out successful transmissions, which could take inordinately large amounts of time to complete. One way to reduce congestion would be to split a single segment into multiple segments, thus creating multiple collision domains. This solution creates a different problem, as now these now separate segments are not able to share information with each other.

Bridges

To alleviate problems with segmentation, Ethernet networks implemented bridges. Bridges connect two or more network segments, increasing the network diameter as a repeater does, but bridges also help regulate traffic. They can send and receive transmissions just like any other node, but they do not function the same as a normal node. The bridge does not originate any traffic of its own; like a repeater, it only echoes what it hears from other stations. (That last statement is not entirely accurate: Bridges do create a special Ethernet frame that allows them to communicate with other bridges, but that is outside the scope of this article.)

Remember how the multiple access and shared medium of Ethernet meant that every station on the wire received every transmission, whether it was the intended recipient or not? Bridges make use of this feature to relay traffic between segments. In the figure above, the bridge connects segments 1 and 2. If station A or B were to transmit, the bridge would also receive the transmission on segment 1. How should the bridge respond to this traffic? It could automatically transmit the frame onto segment 2, like a repeater, but that would not relieve congestion, as the network would behave like one long segment.

One goal of the bridge is to reduce unnecessary traffic on both segments. It does this by examining the destination address of the frame before deciding how to handle it. If the destination address is that of station A or B, then there is no need for the frame to appear on segment 2. In this case, the bridge does nothing. We can say that the bridge filters or drops the frame. If the destination address is that of station C or D, or if it is the broadcast address, then the bridge will transmit, or forward the frame on to segment 2. By forwarding packets, the bridge allows any of the four devices in the figure to communicate. Additionally, by filtering packets when appropriate, the bridge makes it possible for station A to transmit to station B at the same time that station C transmits to station D, allowing two conversations to occur simultaneously!

Switches are the modern counterparts of bridges, functionally equivalent but offering a dedicated segment for every node on the network (more on switches later in the article).

Routers: Logical Segmentation

Bridges can reduce congestion by allowing multiple conversations to occur on different segments simultaneously, but they have their limits in segmenting traffic as well.

An important characteristic of bridges is that they forward Ethernet broadcasts to all connected segments. This behavior is necessary, as Ethernet broadcasts are destined for every node on the network, but it can pose problems for bridged networks that grow too large. When a large number of stations broadcast on a bridged network, congestion can be as bad as if all those devices were on a single segment.

Routers are advanced networking components that can divide a single network into two logically separate networks. While Ethernet broadcasts cross bridges in their search to find every node on the network, they do not cross routers, because the router forms a logical boundary for the network.

Routers operate based on protocols that are independent of the specific networking technology, like Ethernet or token ring (we'll discuss token ring later). This allows routers to easily interconnect various network technologies, both local and wide area, and has led to their widespread deployment in connecting devices around the world as part of the global Internet.

Switched Ethernet

Modern Ethernet implementations often look nothing like their historical counterparts. Where long runs of coaxial cable provided attachments for multiple stations in legacy Ethernet, modern Ethernet networks use twisted pair wiring or fiber optics to connect stations in a radial pattern. Where legacy Ethernet networks transmitted data at 10 megabits per second (Mbps), modern networks can operate at 100 or even 1,000 Mbps!

Perhaps the most striking advancement in contemporary Ethernet networks is the use of switched Ethernet. Switched networks replace the shared medium of legacy Ethernet with a dedicated segment for each station. These segments connect to a switch, which acts much like an Ethernet bridge, but can connect many of these single station segments. Some switches today can support hundreds of dedicated segments. Since the only devices on the segments are the switch and the end station, the switch picks up every transmission before it reaches another node. The switch then forwards the frame over the appropriate segment, just like a bridge, but since any segment contains only a single node, the frame only reaches the intended recipient. This allows many conversations to occur simultaneously on a switched network.

What is Windows Registry??

2009-03-13T06:51:00.000-07:00

What is Registry?

Ans.) First we will know that what is registry,and how is the registry important. Registry is an important in a computer. It depends up on the operating system that we are using.In windows, the default settings are stored in the registry. Also third party softwares store their setting in the registry. Softwares store their settings like window width,last used file in software etc.

The type of the registry values available are :

1. string value
2. binary value
3. DWORD value
4. multi-string value
5. expandable string value

Windows Registry is an enormous batch of files containing information about almost everything that occurs on the computer, from a visit to a Web site to a program installation. The registry also contains information about drivers and other essential programs, like DLLs -- small helper programs that often work with more than one application. This information is stored in the form of "keys" that help programs run. It's like a big blueprint for where everything goes on your computer and how it all fits together. Only computers running Windows operating systems have registries, and despite rumors to the contrary, Windows 7 will have a registry.

A registry may have hundreds of thousands of entries, and new entries are created all the time. As it fills with information, the registry may cause a computer's performance to suffer. One problem is that Windows almost never removes registry entries, even if a program is uninstalled, as most uninstallers aren't able to effectively remove their own registry keys. And as files are moved around and programs are uninstalled, some registry keys point to programs or files that no longer exist or are located elsewhere.

Fortunately, these errors don't have to be tolerated. The registry can be cleaned up, though not completely. And for your troubles, you may get better performance and decreased boot time. Some satisfied users report fewer instances of lag or Windows hanging (when the computer isn't responding). The exact performance boost varies depending on the state of the registry and the effectiveness of the cleaner program employed. You may also free up disk space, although most registry entries are very small.

Default Registry looks like this:

Where are the Windows Registry files?

If you have Windows 9x or ME, known as the 9x Platform, the Registry files are stored in the Windows folder. They are named System.dat and User.dat. However, Windows ME also has Classes.dat. These files all have Hidden attributes so unless you are view hidden files you will not find them.

If you have Windows NT, 2000, 2003, Xp or Vista, known as the NT Platform, the Registry files are stored in their own folder; Windows\System32\Config. You will not be able to copy these files to make backups, as the operating system is protecting them for security reasons.
Lets start with an explanation of the Registry Keys.

Open RegEdit, you'll see the six Hives on the Windows 9x Platform and five on the NT Platform under the "My Computer" header:

HKEY_CLASSES_ROOT: Contains software settings about the file system, it contains shortcut information, and other user interface information. There will be a SubKey for every file association. And each Key here points to another key. The entire Hive is part of HKEY_LOCAL_MACHINE and can be found at HKEY_LOCAL_MACHINE\Software\Classes. If you change a setting in either of these two locations it is also changed in the other.

HKEY_CURRENT_USER: Contains the information for the currently logged-on user, such as settings and software information. Setting changed in this Hive will only affect the current user. This Hive is part of the HKEY_USERS hive.
1) AppEvents Key: contains the settings for which sounds to play for system sound events
2) Control Panel Key: Control Panel settings are stored here, similar to system.ini and win.ini in Win 3.x.
3) InstallLocationsMRU: contains folder paths and drives
4) Keyboard layout: specifies current keyboard layout
5) Network: Network connection information
6) RemoteAccess: Contains information about the current log-on location using Dial-Up Networking
7) Software: Software configuration settings for the currently logged-on user.
You may find other Keys here placed by other software, that is probably should have been placed in one of the above Sub-Keys. The entire Hive is also found at the HKEY_USERS\.Default or if more then one profile HKEY_USERS\(Profile name). If you change and setting in either of these two locations it is also changed in the other.
HKEY_LOCAL_MACHINE: Contains information about the hardware and software settings that are used for all users of this computer.
1) Config: Configuration information . Same as the Hive HKEY_CURRENT_CONFIG on Windows 9x
2) Enum: Hardware information (found under System in NT)
3) Hardware: Information passed to Windows from the BIOS (found under System in NT)
4) Network: information about networks installed to the machine.
5) Security: network security settings.
6) Software: Software-specific information and settings
7) System: System startup and device driver information, and operating system settings.

HKEY_USERS: Information about for each user that logs onto this computer is stored here. Each user will have a Sub-Key under this heading. On Windows 9x, if there is only one user, the SubKey will be ".default". When a user logs on, one of the Sub-Keys will be loaded to the HKEY_CURRENT_USER key.
HKEY_CURRENT_CONFIG : Contains info about the current hardware configuration, pointing to HKEY_LOCAL_MACHINE\Config. This hive is dynamic, meaning it is built on the fly.
HKEY_DYN_DATA: This key contains dynamic information about plug-n-play devices. The data here changes constantly. This key is rewritten every time you boot up, it is a virtual Hive. This Hive is dynamic, meaning it is built on the fly and is not used on the NT Platform.
How Windows uses the Registry

For reference:

HKCU=HKEY_CURRENT_USER
HKLM=HKEY_LOCAL_MACHINE

First you need to understand that the Shell of Windows is the Windows Explorer. Without the Explorer there is no Windows, No desktop and so on.

With Windows loaded and you are logged on, Windows now can use the information in the Registry that each Hive contains. Here is a sample of how the Registry is used.

So let's click on the Start button, which is controlled be the Explorer.exe. Now Windows reads the Key HKCU\ Microsoft\ Windows\ CurrentVersion\ Policies Keys to determine what the current user is allowed to do. What the user is allowed to access. Now scroll up to the Programs label and the Key HKCU\ Microsoft\ Windows\ CurrentVersion\ Explorer is read to determine how Windows will react. Now you open the Start menu and it opens, then you click on a program you wish to open. This is a shortcut that you are clicking on. A shortcut is a file with the extension ".lnk" so Windows now looks at the HKLM\Software\Classes Key for the extension ".lnk" which reads "lnkfile". So Windows now looks for HKLM\Software\Classes\lnkfile which read "ShortCut" and it sees "NeverShowEx" = "" which means do not display file extension for this type of file extension. Windows then looks to see what SubKeys are there and it finds a CLSID SubKey which points to "{00021401- 0000- 0000- C000- 000000000046}". Since the SubKey was "CLSID" Windows knows to look at HKLM\Software\Classes\CLSID Key and finds the matching SubKey. This Key also read "ShortCut" and Windows now looks for what SubKeys are available. It find the "ProgID" Key which points back to the "lnkfile" Key. and it find the server file at the "InProcServer32" file. So Windows now knows to serve this file to Shell32.dll.

If the Explorer did not find the CLSID key listed it would have to search the CLSID Keys for a matching ProgID Key that pointed to the "lnkfile" Key.

Shell32.dll now takes over, the Explorer makes an API call to the Shell32.dll and tells it to Shell (run, start) the file that the that you clicked on. Now the Shell32 knows that this is a ShortCut so it reads the file and determines that you wish to activate the program QikFix. So it starts QikFix now needs an starts loading the other DLLs it needs to run. QikFix searches its' own directory and if not found there looks to the Windows Folder then the System folder. It finds the DLLs it knows it need to run, and then now sees that it needs an interface. So as with all Visual Basic programs it need the Msvbvm50.Dll or Msvbvm60.Dll to do the work for it. So then Msvbvm50.dll draws the plain window and then starts adding the text boxes and the tabs. To do this is may need help form another dll as with the case of the tabs. It knows it needs tabclt32.ocx because when I selected to use the tabs I need to include the DLL name in my source code, which in this case is an Active X control (ocx). Now it needs to draw Tabs but the Msvbvm50.dll has no idea what a tab is.

If there where TypeLib Keys under the CLSID Key then the Explorer would also got read the matching HKLM\Software\Classes\TypeLib Key. The TypeLib Key may point to an Interface Key (HKLM\Software\Classes\Interface) and this Key will tell the Explorer what version is available and so on. To understand more you need to read the next section about SubKeys.
Explanation of SubKeys

You will find a vast amount of different SubKeys, some are user (read) only by the software program, while most of the SubKeys are read by Windows.

The Heart of Windows

The Registry works the same on both the Windows 9x platform, and the NT Platform. However it is laid out a little differently, especially when it comes to the hardware.

The real heart of the Windows Registry is found at the Key:

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows, controlling the software. The System Drivers are controlled at HKEY_LOCAL_MACHINE\System. The hardware is controlled at HKEY_LOCAL_MACHINE\Enum in Windows 9x and ME And HKEY_LOCAL_MACHINE\System\CurrentControlSet\Enum in the NT Platform.

How to clean Computer Registry :

Cleaning Registry:

Registry cleaning is not without risks. This is a very sensitive area of your computer, and if you're happy with how your computer is running, don't go digging around. Trying to manually edit your registry can create errors in the registry that make it impossible to load Windows. Some registry-cleaning programs have been known to delete important registry keys or essential DLL files. And the performance improvements may be negligible, while running the program and approving each recommended deletion could take hours. In addition, reliable data on how registry cleaners affect performance are almost impossible to find. Most "performance tests" are actually produced by the developers of registry-cleaning tools.

Despite these concerns, it is possible to clean out some of the registry's gunk, and your computer may be better off for it. On the next page, we'll take a look at how to go about this delicate job.

Before you mess around with the registry, it's best to to create a backup copy of the registry and to also save any important data to an external hard drive or disk. Some registry-cleaning programs have a feature to back up a copy of your system's registry. If not, a simple Internet search should lead you to a free backup program.

Windows has a built-in program for editing the registry. It's creatively titled regedit.exe and can be accessed by going to the Start menu, clicking Run and typing in the program name. While this program is easy to access, it's difficult to use. Registry entries have long, oblique names that don't say much about what they represent. Even savvy computer users may have no idea what a particular entry points to. So unless you have specific instructions for how to alter or delete a clearly defined entry, it's best not to experiment with regedit.exe.

Third-party registry-cleaner programs are plentiful and remove a lot of the confusing grunt work of parsing and deleting registry entries. To find a program that suits you, check reviews on sites like ZDNet, CNET, PC World or PC Magazine. Some of these programs are free or only fix a few entries at a time, which can be quite laborious when a registry may have 2,000 broken entries. Others may cost $20 or more and may come as part of a package of system utilities.

It's not necessary to clean a registry more than once a month. Using a disk defrag program may provide additional performance boosts.

Before you run the program you've chosen, make sure you close all other open programs, as well as those running in the system tray, next to the clock in the bottom right corner of your screen. Follow directions closely: Most of these cleaner programs are intuitive, first scanning the registry for errors and then offering choices to fix broken entries, but you may miss an important step or warning if you click madly and try to speed through the process.

Some experts recommend against using programs that automatically delete registry errors . Instead, it's better to approve deletions manually. The cleaner will likely offer a list of registry entries that it's safe to delete because they are certainly obsolete. It may also provide an option to "repair" an entry. Going deeper and deleting borderline entries could affect a program's ability to function, such as by deleting a DLL that the cleaner doesn't realize is shared by more than one program -- or you may irreparably damage your installation of Windows. When in doubt, let the entry stay.

And that's about it. Hopefully you managed to clean up a few hundred entries without bricking your computer. If not, well, then you probably can't read this anymore and won't be interested in the links on the next page about registry cleaners and other related topics.

Bluetooth Technology

2009-03-12T05:39:00.000-07:00

Introduction

When you use computers, entertainment systems or telephones, the various pieces and parts of the systems make up a community of electronic devices. These devices communicate with each other using a variety of wires, cables, radio signals and infrared light beams, and an even greater variety of connectors, plugs and protocols. Bluetooth is a wireless protocol for exchanging data over short distances from fixed and mobile devices, creating personal area networks (PANs). It can connect several devices, overcoming problems of synchronization.

There are lots of different ways that electronic devices can connect to one another. For example:

Component cables
Electrical wires
Ethernet cables
Wi-Fi
Infrared signals

Where it is used ?

Bluetooth is a standard and communications protocol primarily designed for low power consumption, with a short range (power-class-dependent: 1 meter, 10 meters, 100 meters) based on low-cost transceiver microchips in each device. Bluetooth makes it possible for these devices to communicate with each other when they are in range. Because the devices use a radio (broadcast) communications system, they do not have to be in line of sight of each other.

Class	Maximum Permitted Power mW (dBm)	Range (approximate)

Class 1	100 mW (20 dBm)	~100 meters
Class 2	2.5 mW (4 dBm)	~10 meters
Class 3	1 mW (0 dBm)	~1 meter

In most cases the effective range of class 2 devices is extended if they connect to a class 1 transceiver, compared to a pure class 2 network. This is accomplished by the higher sensitivity and transmission power of Class 1 devices.

Version	Data Rate
Version 1.2	1 Mbit/s
Version 2.0 + EDR	3 Mbit/s
WiMedia Alliance (proposed)	53 - 480 Mbit/s

Specifications and features

The Bluetooth specification was developed in 1994 by Jaap Haartsen and Sven Mattisson, who were working for Ericsson Mobile Platforms in Lund, Sweden. The specification is based on frequency-hopping spread spectrum technology.

The specifications were formalized by the Bluetooth Special Interest Group (SIG). The SIG was formally announced on May 20, 1998.

Bluetooth 1.0 and 1.0B

Versions 1.0 and 1.0B had many problems, and manufacturers had difficulty making their products interoperable. Versions 1.0 and 1.0B also included mandatory Bluetooth hardware device address (BD_ADDR) transmission in the Connecting process (rendering anonymity impossible at the protocol level), which was a major setback for certain services planned for use in Bluetooth environments.

Bluetooth 1.1

* Ratified as IEEE Standard 802.15.1-2002.
* Many errors found in the 1.0B specifications were fixed.
* Added support for non-encrypted channels.
* Received Signal Strength Indicator (RSSI).

Bluetooth 1.2

This version is backward compatible with 1.1 and the major enhancements include the following:

Faster Connection and Discovery
Higher transmission speeds in practice, up to 721 kbit/s, than in 1.1.
Extended Synchronous Connections (eSCO), which improve voice quality of audio links.
Host Controller Interface (HCI) support for three-wire UART.
Ratified as IEEE Standard 802.15.1-2005.

Bluetooth 2.0

This version of the Bluetooth specification was released on November 10, 2004. It is backward compatible with the previous version 1.1. The main difference is the introduction of an Enhanced Data Rate (EDR) for faster data transfer. The nominal rate of EDR is about 3 megabits per second, although the practical data transfer rate is 2.1 megabits per second.

According to the 2.0 specification, EDR provides the following benefits:

Three times faster transmission speed — up to 10 times (2.1 Mbit/s) in some cases.
Reduced complexity of multiple simultaneous connections due to additional bandwidth.
Lower power consumption through a reduced duty cycle.

Bluetooth 2.0

Bluetooth Core Specification Version 2.1 is fully backward compatible with 1.1, and was adopted by the Bluetooth SIG on July 26, 2007. This specification includes the following features:

Extended inquiry response: provides more information during the inquiry procedure to allow better filtering of devices before connection.
Sniff subrating: reduces the power consumption when devices are in the sniff low-power mode, especially on links with asymmetric data flows.
Encryption Pause Resume: enables an encryption key to be refreshed, enabling much stronger encryption for connections that stay up for longer than 23.3 hours (one Bluetooth day).
Secure Simple Pairing: radically improves the pairing experience for Bluetooth devices, while increasing the use and strength of security. It is expected that this feature will significantly increase the use of Bluetooth.
Near Field Communication (NFC) cooperation: automatic creation of secure Bluetooth connections when NFC radio interface is also available. This functionality is part of the Secure Simple Pairing where NFC is one way of exchanging pairing information.

How Bluetooth Creates a Connection

Bluetooth takes small-area networking to the next level by removing the need for user intervention and keeping transmission power extremely low to save battery power.

Bluetooth is essentially a networking standard that works at two levels:

It provides agreement at the physical level -- Bluetooth is a radio-frequency standard.
It provides agreement at the protocol level, where products have to agree on when bits are sent, how many will be sent at a time, and how the parties in a conversation can be sure that the message received is the same as the message sent.

Bluetooth wireless PC card

Any Bluetooth device will transmit the following information on demand:

Device name.
Device class.
List of services.
Technical information, for example, device features, manufacturer, Bluetooth specification used, clock offset.

Any device may perform an inquiry to find other devices to connect to, and any device can be configured to respond to such inquiries. However, if the device trying to connect knows the address of the device, it always responds to direct connection requests and transmits the information shown in the list above if requested. Use of a device's services may require pairing or acceptance by its owner, but the connection itself can be initiated by any device and held until it goes out of range.

How Bluetooth Operates

Bluetooth networking transmits data via low-power radio waves. It communicates on a frequency of 2.45 gigahertz (actually between 2.402 GHz and 2.480 GHz, to be exact). This frequency band has been set aside by international agreement for the use of industrial, scientific and medical devices (ISM).

One of the ways Bluetooth devices avoid interfering with other systems is by sending out very weak signals of about 1 milliwatt. By comparison, the most powerful cell phones can transmit a signal of 3 watts. The low power limits the range of a Bluetooth device to about 10 meters (32 feet).

Bluetooth can connect up to eight devices simultaneously. With all of those devices in the same 10-meter (32-foot) radius, you might think they'd interfere with one another, but it's unlikely. Bluetooth uses a technique called spread-spectrum frequency hopping that makes it rare for more than one device to be transmitting on the same frequency at the same time. In this technique, a device will use 79 individual, randomly chosen frequencies within a designated range, changing from one to another on a regular basis. In the case of Bluetooth, the transmitters change frequencies 1,600 times every second, meaning that more devices can make full use of a limited slice of the radio spectrum.

When Bluetooth-capable devices come within range of one another, an electronic conversation takes place to determine whether they have data to share or whether one needs to control the other. The user doesn't have to press a button or give a command -- the electronic conversation happens automatically. Once the conversation has occurred, the devices -- whether they're part of a computer system or a stereo -- form a network.

Bluetooth Security

In any wireless networking setup, security is a concern. Devices can easily grab radio waves out of the air, so people who send sensitive information over a wireless connection need to take precautions to make sure those signals aren't intercepted. Bluetooth technology is no different -- it's wireless and therefore susceptible to spying and remote access.

Bluetooth offers several security modes, and device manufacturers determine which mode to include in a Bluetooth-enabled gadget. In almost all cases, Bluetooth users can establish "trusted devices" that can exchange data without asking permission. When any other device tries to establish a connection to the user's gadget, the user has to decide to allow it. Service-level security and device-level security work together to protect Bluetooth devices from unauthorized data transmission. Security methods include authorization and identification procedures that limit the use of Bluetooth services to the registered user and require that users make a conscious decision to open a file or accept a data transfer. As long as these measures are enabled on the user's phone or other device, unauthorized access is unlikely. A user can also simply switch his Bluetooth mode to "non-discoverable" and avoid connecting with other Bluetooth devices entirely. If a user makes use of the Bluetooth network primarily for synching devices at home, this might be a good way to avoid any chance of a security breach while in public.

Health concerns

Bluetooth uses the microwave radio frequency spectrum in the 2.4 GHz to 2.4835 GHz range. Maximum power output from a Bluetooth radio is 100 mW, 2.5 mW, and 1 mW for Class 1, Class 2, and Class 3 devices respectively, which puts Class 1 at roughly the same level as mobile phones, and the other two classes much lower. Accordingly, Class 2 and Class 3 Bluetooth devices are considered less of a potential hazard than mobile phones, and Class 1 may be comparable to that of mobile phones.

What is WiFi--How it works ??

2009-03-11T09:33:00.000-07:00

What Is WiFi?

A wireless network uses radio waves, just like cell phones, televisions and radios do. In fact, communication across a wireless network is a lot like two-way radio communication.

Here's what happens:

1.) A computer's wireless adapter translates data into a radio signal and transmits it using an antenna.
2.) A wireless router receives the signal and decodes it. The router sends the information to the Internet using a physical, wired Ethernet connection.

What's in a name?

You may be wondering why people refer to WiFi as 802.11 networking. The 802.11 designation comes from the IEEE. The IEEE sets standards for a range of technological protocols, and it uses a numbering system to classify these standards.
The process also works in reverse, with the router receiving information from the Internet, translating it into a radio signal and sending it to the computer's wireless adapter.

The radios used for WiFi communication are very similar to the radios used for walkie-talkies, cell phones and other devices. They can transmit and receive radio waves, and they can convert 1s and 0s into radio waves and convert the radio waves back into 1s and 0s. But WiFi radios have a few notable differences from other radios :

wifi network system

* They transmit at frequencies of 2.4 GHz or 5 GHz. This frequency is considerably higher than the frequencies used for cell phones, walkie-talkies and televisions. The higher frequency allows the signal to carry more data.

* They use 802.11 networking standards, which come in several flavors:

802.11a transmits at 5 GHz and can move up to 54 megabits of data per second. It also uses orthogonal frequency-division multiplexing (OFDM), a more efficient coding technique that splits that radio signal into several sub-signals before they reach a receiver. This greatly reduces interference.
802.11b is the slowest and least expensive standard. For a while, its cost made it popular, but now it's becoming less common as faster standards become less expensive. 802.11b transmits in the 2.4 GHz frequency band of the radio spectrum. It can handle up to 11 megabits of data per second, and it uses complementary code keying (CCK) modulation to improve speeds.
802.11g transmits at 2.4 GHz like 802.11b, but it's a lot faster -- it can handle up to 54 megabits of data per second. 802.11g is faster because it uses the same OFDM coding as 802.11a.
802.11n is the newest standard that is widely available. This standard significantly improves speed and range. For instance, although 802.11g theoretically moves 54 megabits of data per second, it only achieves real-world speeds of about 24 megabits of data per second because of network congestion. 802.11n, however, reportedly can achieve speeds as high as 140 megabits per second. The standard is currently in draft form -- the Institute of Electrical and Electronics Engineers (IEEE) plans to formally ratify 802.11n by the end of 2009.

* Other 802.11 standards focus on specific applications of wireless networks, like wide area networks (WANs) inside vehicles or technology that lets you move from one wireless network to another seamlessly.

* WiFi radios can transmit on any of three frequency bands. Or, they can "frequency hop" rapidly between the different bands. Frequency hopping helps reduce interference and lets multiple devices use the same wireless connection simultaneously.

Access points

As long as they all have wireless adapters, several devices can use one router to connect to the Internet. This connection is convenient, virtually invisible and fairly reliable; however, if the router fails or if too many people try to use high-bandwidth applications at the same time, users can experience interference or lose their connections.

Next, we'll look at how to connect to the Internet from a WiFi hotspot.

WiFi Hotspots

If you want to take advantage of public WiFi hotspots or start a wireless network in your home, the first thing you'll need to do is make sure your computer has the right gear. Most new laptops and many new desktop computers come with built-in wireless transmitters. If your laptop doesn't, you can buy a wireless adapter that plugs into the PC card slot or USB port. Desktop computers can use USB adapters, or you can buy an adapter that plugs into the PCI slot inside the computer's case. Many of these adapters can use more than one 802.11 standard.

Wireless adapters can plug into a computer's PC card slot or USB port.

Once you've installed your wireless adapter and the drivers that allow it to operate, your computer should be able to automatically discover existing networks. This means that when you turn your computer on in a WiFi hotspot, the computer will inform you that the network exists and ask whether you want to connect to it. If you have an older computer, you may need to use a software program to detect and connect to a wireless network.

Being able to connect to the Internet in public hotspots is extremely convenient. Wireless home networks are convenient as well. They allow you to easily connect multiple computers and to move them from place to place without disconnecting and reconnecting wires. In the next section, we'll look at how to create a wireless network in your home.

How WiFi Works :

Building a Wireless Network

If you already have several computers networked in your home, you can create a wireless network with a wireless access point. If you have several computers that are not networked, or if you want to replace your Ethernet network, you'll need a wireless router. This is a single unit that contains:

1. A port to connect to your cable or DSL modem
2. A router
3. An Ethernet hub
4. A firewall
5. A wireless access point

A wireless router allows you to use wireless signals or Ethernet cables to connect your computers to one another, to a printer and to the Internet. Most routers provide coverage for about 100 feet (30.5 meters) in all directions, although walls and doors can block the signal. If your home is very large, you can buy inexpensive range extenders or repeaters to increase your router's range.

A wireless router uses an antenna to send signals to wireless devices and a wire to send signals to the Internet

A wireless router uses an antenna to send signals to wireless devices and a wire to send signals to the Internet.

As with wireless adapters, many routers can use more than one 802.11 standard. 802.11b routers are slightly less expensive, but because the standard is older, they're slower than 802.11a, 802.11g and 802.11n routers. Most people select the 802.11g option for its speed and reliability.

Once you plug in your router, it should start working at its default settings. Most routers let you use a Web interface to change your settings. You can select:

* The name of the network, known as its service set identifier (SSID) -- The default setting is usually the manufacturer's name.
* The channel that the router uses -- Most routers use channel 6 by default. If you live in an apartment and your neighbors are also using channel 6, you may experience interference. Switching to a different channel should eliminate the problem.
* Your router's security options -- Many routers use a standard, publicly available sign-on, so it's a good idea to set your own username and password.

Security is an important part of a home wireless network, as well as public WiFi hotspots. If you set your router to create an open hotspot, anyone who has a wireless card will be able to use your signal. Most people would rather keep strangers out of their network, though. Doing so requires you to take a few security precautions.

It's also important to make sure your security precautions are current. The Wired Equivalency Privacy (WEP) security measure was once the standard for WAN security. The idea behind WEP was to create a wireless security platform that would make any wireless network as secure as a traditional wired network. But hackers discovered vulnerabilities in the WEP approach, and today it's easy to find applications and programs that can compromise a WAN running WEP security.

To keep your network private, you can use one of the following methods:

* WiFi Protected Access (WPA) is a step up from WEP and is now part of the 802.11i wireless network security protocol. It uses Temporal Key Integrity Protocol (TKIP) encryption. As with WEP, WPA security involves signing on with a password. Most public hotspots are either open or use WPA or 128-bit WEP technology, though some still use the vulnerable WEP approach.

* Media Access Control (MAC) address filtering is a little different from WEP or WPA. It doesn't use a password to authenticate users -- it uses a computer's physical hardware. Each computer has its own unique MAC address. MAC address filtering allows only machines with specific MAC addresses to access the network. You must specify which addresses are allowed when you set up your router. This method is very secure, but if you buy a new computer or if visitors to your home want to use your network, you'll need to add the new machines' MAC addresses to the list of approved addresses. The system isn't foolproof. A clever hacker can spoof a MAC address -- that is, copy a known MAC address to fool the network that the computer he or she is using belongs on the network.

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