Compact Disc,Read -Only-Memory (C-D ROM )

CD-ROM (Compact Disc, read-only-memory) is an adaptation of the CD that is designed to store computer data in the form of text and graphics, as well as hi-fi stereo sound. The original data format standard was defined by Philips and Sony in the 1983 Yellow Book. Other standards are used in conjunction with it to define directory and file structures, including ISO 9660, HFS (Hierarchal File System, for Macintosh computers), and Hybrid HFS-ISO. Format of the CD-ROM is the same as for audio CDs: a standard CD is 120 mm (4.75 inches) in diameter and 1.2 mm (0.05 inches) thick and is composed of a polycarbonate plastic substrate (underlayer - this is the main body of the disc), one or more thin reflective metal (usually aluminum) layers, and a lacquer coating.

The Yellow Book specifications were so general that there was some fear in the industry that multiple incompatible and proprietary formats would be created. In order to prevent such an occurrence, representatives from industry leaders met at the High Sierra Hotel in Lake Tahoe to collaborate on a common standard. Nicknamed the High Sierra Format, this version was later modified to become ISO 9660. Today, CD-ROMs are standardized and will work in any standard CD-ROM drive. CD-ROM drives can also read audio compact discs for music, although CD players cannot read CD-ROM discs.

CD-ROM Data Storage

Although the disc media and the drives of the CD and CD-ROM are, in principle, the same, there is a difference in the way data storage is organized. Two new sectors were defined, Mode 1 for storing computer data and Mode 2 for compressed audio or video/graphic data.

CD-ROM Mode 1

CD-ROM Mode 1 is the mode used for CD-ROMs that carry data and applications only. In order to access the thousands of data files that may be present on this type of CD, precise addressing is necessary. Data is laid out in nearly the same way as it is on audio disks: data is stored in sectors (the smallest separately addressable block of information), which each hold 2,352 bytes of data, with an additional number of bytes used for error detection and correction, as well as control structures. For mode 1 CD-ROM data storage, the sectors are further broken down, and 2,048 used for the expected data, while the other 304 bytes are devoted to extra error detection and correction code, because CD-ROMs are not as fault tolerant as audio CDs. There are 75 sectors per second on the disk, which yields a disc capacity of 681,984,000 bytes (650MB) and a single speed transfer rate of 150 KBps, with higher rates for faster CD-ROM drives. Drive speed is expressed as multiples of the single speed transfer rate, as 2X, 4X, 6X, and so on. Most drives support CD-ROM XA (Extended Architecture) and Photo-CD (including multiple session discs).

CD-ROM Mode 2

CD-ROM Mode 2 is used for compressed audio/video information and uses only two layers of error detection and correction, the same as the CD-DA. Therefore, all 2,336 bytes of data behind the sync and header bytes are for user data. Although the sectors of CD-DA, CD-ROM Mode 1 and Mode 2 are the same size, the amount of data that can be stored varies considerably because of the use of sync and header bytes, error correction and detection. The Mode 2 format offers a flexible method for storing graphics and video. It allows different kinds of data to be mixed together, and became the basis for CD-ROM XA. Mode 2 can be read by normal CD-ROM drives, in conjunction with the appropriate drivers.

Data Encoding and Reading

The CD-ROM, like other CD adaptations, has data encoded in a spiral track beginning at the center and ending at the outermost edge of the disc. The spiral track holds approximately 650 MB of data. That's about 5.5 billion bits. The distance between two rows of pits, measured from the center of one track to the center of the next track is referred to as track pitch. The track pitch can range from 1.5 to 1.7 microns, but in most cases is 1.6 microns.

Constant Linear Velocity (CLV) is the principle by which data is read from a CD-ROM. This principal states that the read head must interact with the data track at a constant rate, whether it is accessing data from the inner or outermost portions of the disc. This is affected by varying the rotation speed of the disc, from 500 rpm at the center, to 200 rpm at the outside. In a music CD, data is read sequentially, so rotation speed is not an issue. The CD-ROM, on the other hand, must read in random patterns, which necessitates constantly shifting rotation speeds. Pauses in the read function are audible, and some of the faster drives can be quite noisy because of it.

• CD-ROM drives are necessary today for most programs. A single CD can store up to 650 MB of data (newer CD-Rs allow for 700 MB of data, perhaps more with "overburn"). Fast CD-ROM drives have been a big topic in the past, but all of today's CD-ROM drives are sufficiently fast. Of course, it's nice to have the little bits of extra speed. However, when you consider CD-ROM drives are generally used just to install a program or copy CDs, both of which are usually done rarely on most users' computers, the extra speed isn't usually very important. The speed can play a big role if you do a lot of CD burning at high speeds or some audio extraction from audio CDs (i.e. converting CDs to MP3s).
• CD-R/RW (which stands for Recordable / ReWritable) drives (aka burners, writers) allow a user to create their own CDs of audio and/or data. These drives are great for backup purposes (backup your computer's hard drive or backup your purchased CDs) and for creating your own audio CD compilations (not to mention other things like home movies, multimedia presentations, etc.).
• DVD-ROM drives can store up to 4 GB of data or about 6 times the size of a regular CD (not sure on the exact size, but suffice to say it's a very large storage medium). DVDs look about the same and are the same size as a CD-ROM. DVD drives can also read CD-ROM drives, so you don't usually need a separate CD-ROM drive. DVD drives have become low enough inprice that there isn't much point in purchasing a CD-ROM drive instead of a DVD-ROM drive. Some companies even make CD burner drives that will also read DVDs (all in one). DVD's most practical use is movies. The DVD format allows for much higher resolution digital recording that looks much clearer than VCR recordings.
• DVD recordable drives are available in a couple of different formats - DVD-R or DVD+R with a RW version of each. These are slightly different discs and drives (although some drives support writing to both formats). One is not much better than the other, so it really boils down to price of the media (and also availability of the media).

Universal Serial Bus (USB)

USB - Universal Serial Bus - is a standard for connecting additional equipment to your computer, like printers, scanners, webcam's, digital camera's, keyboards, mouse, harddisks, etc.

It was supposed to solve all the confusion and issues on PC ports. Well it didn't ... as with all standards: confusion became even worse.

Apple introduced a similar product years ago called FireWire, the direct competition of USB 2.0. That's not all, within the USB standard we also have USB 1.1, USB 2.0, HiSpeed, FullSpeed, and LowSpeed.

So what now?

Tip: not all Windows versions can deal with USB ports, for example Windows 95 and Windows NT 4.0.

Tip: Keep in mind that your BIOS, by default, does not support a USB keyboard. Menaing: that if you boot your PC while having a USB keyboard, you will NOT be able to modify anything! As a matter of fact: you won't even be able to get in to the BIOS! So first sue your old PS/2 keyboard to go into the BIOS and set "USB Keyboard Support" to enabled!

Today just about every PC comes with Universal SerialBus, or USB ports. In fact, many computers will even have additional USB ports located on the front of the tower, in additional to two standard USB ports at the back. In the late 1990s, a few computer manufacturers started including USB support in their new systems, but today USB has become a standard connection port for many devices such as keyboards, mice, joysticks and digital cameras to name but a few USB-enabled devices. USB is able to support and is supported by a large range of products. Adding to the appeal of USB is that it is supported at the operating system level, and compared to alternative ports such aspraallel orserial ports, USB is very user-friendly. When USB first started appearing in the marketplace, it was (and still is) referred to as a plug-and-play port because of its ease of use. Consumers without a lot of technical or hardware knowledge were able to easily connect USB devices to their computer. You no longer needed to turn the computer off to install the devices either. You simply plug them in and go. USB devices can also be used across multiple platforms. USB works on Windows andMac, plus can be used with other operating systems, such as Linux, for example, with a reliable degree of success. Before USB, connecting devices to your system was often a hassle. Modems and digital cameras were connected via the serial porlwhich was quite slow, as only 1 bit is transmitted at a time through a serial port. While printers generally required a parallel printer port, which is able to receive more than one bit at a time — that is, it receives several bits in parallel. Most systems provided two serial ports and a parallel printer port. If you had several devices, unhooking one device and setting up the software and drives to use another device could often be problematic for the user. The introduction of USB ended many of the headaches associated with needing to use serial ports and parallel printer ports. USB offered consumers the option to connect up to 127 devices, either directly or through the use of a USBhub. It was much faster since USB supports data transfer rates of 12 Mbps for disk drives and other high-speed throughput and 1.5Mbps for devices that need less bandwidth. Additionally, consumers can literally plug almost any USB device into their computer, and Windows will detect it and automatically set-up the hardware settings for the device. Once that device has been installed you can remove it from your system and the next time you plug it in, Windows will automatically detect it.

USB 1x

First released in 1996, the original USB 1.0standard offered data rates of 1.5 Mbps. The USB 1.1 standard followed with two data rates: 12 Mbps for devices such as disk drives that need high-speed throughput and 1.5 Mbps for devices such as joysticks that need much less bandwidth.

USB 2x

In 2002 a newer specification USB 2.0 also called Hi-Speed USB 2.0, was introduced. It increased the data transfer rate for PC to USB device to 480 Mbps, which is 40 times faster than the USB 1.1 specification. With the increased bandwidth, high throughput peripherals such as digital cameras, CD burners and video equipment could now be connected with USB. It also allowed for multiple high-speed devices to run simultaneously. Another important feature of USB 2.0 is that it supports Windows XP through Windows update.

USB OTG

USB On-the-Go (OTG) addresses the need for devices to communicate directly for mobile connectivity. USB OTG allows consumers to connect mobile devices without a PC. For example, USB OTG lets consumers plug their digital camera directly into a compliant printer and print directly from the camera, removing the need to go through the computer. Similarly, a PDA keyboard with a USB OTG interface can communicatea with any brand PDA that has a USB OTG interface.

USB-OTG also provides limited host capability to communicate with selected other USB peripherals, a small USB connector to fit the mobile form factor and low power features to preserve battery life. USB OTG is a supplement to the USB 2.0 specification.

Types of USB Connectors

Currently, there are four types of USB connectors: Type A, Type B, mini-A and mini-B and are supported by the different USB specifications (USB 1, USB 2 and USB-OTG).

USB A (Host)

Often referred to as the downstream connector, the Type A USB connector is rectangular in shape and is the one you use to plug into the CPU or USB hub.

USB B (Device)

Also called the upstream connector, the Type B USB connector is more box-shaped and is the end that attaches directly to the device (such as a printer or digital camera).

USB 1.1 specifies the Type A and Type B.

Mini-B

The USB 2.0 connector was too large for many of the new handheld devices, such as PDAs and cell phones. The mini-B was introduced to enable consumers to take advantage of USB PC connectivity for these smaller devices.

USB 2.0 specifies the Type A, Type B and mini-B.

Mini-A

With the need to connect mobile devices without the aid of a computer, the mini-A port was designed to connect the new generation of smaller mobile devices.

USB OTG specifies the mini-A.

Certified Wireless USB

With an estimated 2 billion plus USB connected devices in the world and a growing interest in wireless computing, it's no surprise that development has turned to wireless USB. The USB Implementers Forum has introduced Certified Wireless USB the newest extension to the USB technology. Wireless USB applies wireless technology to existing USB standards to enable wireless consumers to still use USB devices without the mess of wires and worry of cords. Still in its infancy, the Wireless USB specifications were made available to the public only in May 2005.

Wireless USB is based on the WiMedia MAConvergence Architecture, using the WiMedia Alliance's MB-OFDM ultra wideband MAC and PHY. It delivers speeds equivalent to wired Hi-Speed USB, with bandwidths of 480Mbs at 3 meters and 110 Mbs at 10 meters.

Computer Mouse

A device that controls the movement of the cursur or pointeron a display pictures A mouse is a small object you can roll along a hard, flat surface. Its name is derived from its shape, which looks a bit like a mouse, its connecting wire that one can imagine to be the mouse's tail, and the fact that one must make it scurry along a surface. As you move the mouse, the pointer on the display screen moves in the same direction. Mice contain at least one button and sometimes as many as three, which have different functions depending on whatprogram is running. Some newer mice also include a scroll wheel for scrolling through long documents.

Invented by Douglas Engelbart of Stanford Research Center in 1963, and pioneered by Xerox in the 1970s, the mouse is one of the great breakthroughs in computerergonomics because it frees the user to a large extent from using thekeyboard In particular, the mouse is important for graphical user interfaces because you can simply point to options and objects andclick a mouse button. Suchapplications are often called point-and-click programs. The mouse is also useful for graphics programs that allow you to draw pictures by using the mouse like a pen, pencil, or paintbrush.

There are three basic types of mice:

1. mechanical: Has a rubber or metal ball on its underside that can roll in all directions. Mechanical sensors within the mouse detect the direction the ball is rolling and move the screen pointer accordingly.
2. optomechanical: Same as a mechanical mouse, but uses optical sensors to detect motion of the ball.
3. optical: Uses a laser to detect the mouse's movement. You must move the mouse along a special mat with a grid so that the optical mechanism has a frame of reference. Optical mice have no mechanical moving parts. They respond more quickly and precisely than mechanical and optomechanical mice, but they are also more expensive.

Many of you will visit us as a part a journey of discovery as to why doing a seemingly simple task like sitting at a computer can have a wide range of life impacting consequences. Hopefully some of you are here in the hope of avoiding such consequences. We cannot tell you how you personally got Carpal Tunnel Syndrome, DeQuervains tendonitis or one of the myriad of conditions that can occur, but we can simply explain why all who use computers that do not understanding a very human condition, fatigue, could develop a condition as a consequence.

We were all designed to Fatigue!

That isn't designed to fail! Fatigue is fundamental to our design to warn us to stop and take a break. Fatigue causes ache, if we do not ache we do not go onto injure (fail).

Back when our design was being honed we seldom sat and did anything for hours and hours a day, and hundreds of days a year. Stone axes were seldom wielded (we suspect) many millions of times a year and a life expectancy of about 30 (possible due to some of those axes) would likely have made the development of chronic conditions less of a worry at that time and so nature may have overlooked the need to adapt us for sitting and working as we do today.

While she did make sure we notice aches and pains she also equipped us to temporarily ignore some of them under certain circumstance. One circumstance she saw most dire was anything "life threatening". Though in preparing us for this she assumed that under such a circumstance we would be "thinking, a lot" and planning our survival moment to moment. Consequently she designed pain and thinking circuits in the brain to overlap so that when we are actively thinking, concentrating, signals received over our pain circuits are "dulled", much like turning down the volume on a fire siren. As we describe it: "falling over to aches or pains too easily in those times could have been the difference between eating lunch and being lunch!" This process, described by brain and migraine researchers, is called Cognitive Distraction and is why when we are busy concentrating we do not notice the warning signs of fatigue so stop awhile, which might help us to avoid many of the clinical conditions that can be directly correlated with it. We view Cognitive Distraction as the "missing link" in the understanding as to why extensive hours of computer work may cause many of the fatigue related syndromes people have to live with today.

Fatigue is a flag as to muscle "supplies" being low. It is caused by a build up of toxic byproducts of our muscle biochemistry. We can continue to work under those circumstances because we are assumed to be in survival mode [CD is a primeval survival mechanism]. But typing that report or surfing the web are likely to be less critical to our long term survival than they are necessary to satiate our short term perception of need. This is a part of the challenge in putting things right. The instinct involved is survival which was not anticipated as being activated by an enduring short term stimulus of need. It is mostly down to us as individuals as to how we cope with all these "opposing forces. Until the first baby is born with a USB port instead of a tummy button we suspect that nature will leave us to sort this one out by ourselves.

Those who do not know of the fatigue issue, or cannot see the benefits of changing the way they have been taught to work since the dawn of the computer mouse will not see a reason to change until it hurts! Much like many only see the benefit of wearing a seatbelt an inch or two from the windscreen they are about to fly through. We are concerned that statistics suggest that that 1 in 3 schoolchildren being taught to use a computer today will likely become impaired to a point of disability before they have repaid their student loans. We are not assuming the passing of mouse laws anytime soon, though one actually does exist in the US and that is a design standard called Section 508, required for all Federal Government purchases. Because there is no direction (ergonomic standards) and little if any clinical research by our industry into the way we work, save for our own AirO2bic mouse/CTS clinical study, anyone can make an "ergonomic product" without the need to explain why it is ergonomic. So in focusing upon what we (you) can do and remembering the fact that we cannot escape from fatigue, we have evolved a comprehensive and cohesive strategy that we call Anti.Fatigue™

Computer Monitor

In computers, a monitor is a computer display and related parts packaged in a physical unit that is separate from other parts of the computer. Notebook computers don't have monitors because all the display and related parts are integrated into the same physical unit with the rest of the computer. In practice, the terms monitor and display are used interchangably.The computer monitor is an output device that is part of your computer's display system. A cable connects the monitor to a video adapter (video card) that is installed in an expansion slot on your computer’s motherboard. This system converts signals into text and pictures and displays them on a TV-like screen (the monitor).

The computer sends a signal to the video adapter, telling it what character, image or graphic to display. The video adapter converts that signal to a set of instructions that tell the display device (monitor) how to draw the image on the screen.

What is a Monitor?

The monitor displays the video and graphics information generated by the computer through the video card. Monitors are very similar to televisions but display information at a much higher quality.

The Monitor is Also Known As

screen, display, video display, video screen

Important Monitor Facts

A monitor, no matter the type, connects to either a VGA or DVI port on a video card. Before investing in a new monitor, make sure that both devices support the same type of connection.

Monitors are not typically user serviceable. For your safety, it's not usually wise to open and work on a monitor.

Popular Monitor Manufacturers

Acer, Hanns-G, LG Electronics, Sceptre

Monitor Description

Monitors are display devices external to the computer case and connect via a cable to a port on the video card. Even though the monitor sits outside the main computer housing, it is an essential part of the complete system.

Monitors come in two major types - CRT and LCD. CRT monitors look much like traditional televisions and are very deep in size. LCD monitors are much thinner while still offering equivalent, if not better, graphics quality. LCD monitors are beginning to obsolete CRT monitors due to their smaller "footprint" on the desk and decreasing price.

Most monitors range in size from 15" to 21" or more. This size is a diagonal measurement from one corner of the screen to the other.

Central Processing Unit (CPU)

CPU is an acronym that stands for central processing unit. The central processing unit is responsible for performing all of the mathematical calculations that are required for a computer to function properly. Because a computer cannot function without the CPU (which may also be referred to as the central processor or just the processor), it is not uncommon to hear people refer to the CPU as the "brains" of a computer.

How does the CPU work?

To properly perform its job, the CPU must complete a cycle of four steps. The first step in this cycle is to fetch a instruction from a software program's memory. Once the CPU fetches the instruction, its second step is to decode the instruction. By decoding the instruction, the CPU is able to organize the information from the instruction in a manner that allows the CPU to complete the next step, which is executing.

During the execution step, the CPU completes the instruction. It accomplishes this by following the information gained during the decoding step. Once the CPU has finished executing the instruction, the final step in this cycle is to write-back the results that occurred during the execution step. The CPU can write-back the results to its own internal register, or to the main memory of the computer.

What companies make CPUs?

While there are numerous companies that make CPUs for different purposes, the two best known makers of CPUs for consumer computers are AMD and Intel. AMD's current line of processors includes Athlon, Phenom, Sempron and Turion processors, while Intel's current line of processors includes the Celeron, Pentium, Core 2, Centrino and Centrino 2 processors.

On large machines, CPUs require one or more printed circuit board. On personal computer and small workstation , the CPU is housed in a single chip called a microprocessor Since the 1970's the microprocessor class of CPUs has almost completely overtaken all other CPU implementations.

The CPU itself is an internal component of the computer. Modern CPUs are small and square and contain multiple metallic connectors or pins on the underside. The CPU is inserted directly into a CPU socket, pin side down, on the motherboard. Each motherboard will support only a specific type or range of CPU so you must check the motherboard manufacturer's specifications before attempting to replace or upgrade a CPU. Modern CPUs also have an attached heatsink and small fan that go directly on top of the CPU to help dissipate heat.

The CPU is Also Known As

processor, microprocessor, central processor, "the brains of the computer"

Important CPU Facts

Not all CPUs have pins on their bottom sides, but in the ones that do, the pins are easily bent. Take great care when handling, especially when installing onto themotherboard

Each motherboard supports only a certain range of CPU types so always check with your motherboard

If you’re in the market for a newcomputer, it’s necessary to understand the function of a CPU. Also known as the Central Processing Unit or processor, the CPU is essentially the “brains” of your computer. Without the CPU, you wouldn’t be able to play games, type research papers, or surf the Internet. Your computer would basically be a very expensive paperweight.

Sometimes people mistakenly believe the case or chassis of a computer is the CPU. However, a CPU is an internal component of the computer. You can’t see it from the outside of the system; you’d have to peek inside and remove both the CPU heatsink and fan to get a good look.

The first CPUs were used in the early 1960s. They were custom designed as part of a larger computer, making them prohibitively expensive. Once engineers figured out how to mass produce the CPU, personal computers became more affordable for the average American. With the introduction of the integrated circuit in the late 1970s, it became possible for smaller CPUs to be manufactured as well. This helped transform computers from large, bulky devices that took up entire rooms to more manageable desktop and laptop models.

Today, Intel is the best-known manufacturer of computer CPUs. No matter what type of computer you have, however, your CPU works by executing a series of stored instructions known as a program. Most CPUs conform to the von Neumann architecture, which says that the CPU must fetch, decode, execute, and writeback the data in a fairly rapid succession.

Since the CPU is one of the most important parts of a computer, it should come as no surprise that it is also the most expensive. In fact, if your computer is more than three years old and your CPU has been damaged by static electricity or some other factor, you may want to consider upgrading to an entirely new computer. A newer, faster CPU will often provide enough additional computing power to make the purchase a wise investment.

CPUs are sometimes called microprocessors, although these two terms are not quite interchangeable. The microprocessor , first introduced in the 1970s, reduces the word size of a CPU from 32 bits to 4 bits in an attempt to allow the transistors of the logic circuits to fit on a single part. Often, it takes more than one microprocessor to perform all of the functions of a CPU. Microprocessors are also commonly used in cell phones, automobiles, and children’s electronic toys.

Computer Keyboard

One of the most common parts of the computer is the keyboard. The most common keyboards used today are the 101-key Enhanced keyboard, the 104-key window keyboard, the 82-key Apple standard keyboard and the 108-ey Apple Extended keyboard. Each of these common keyboards are equipped with external parts and internal parts that combine to perform certain tasks. External parts are the parts that are easily seen on the outside of the keyboard. These parts are the typing keys, the numeric keypad, the function keys and the control keys. The typing keys are just as they sound, they are the alphabet keys that are laid out on the keyboard in the same location, as they would be found on a typewriter. The numeric keypad is found to the right of the typing keys and contains number keys that are laid out the same as a calculator or adding machine. This keypad also contains the direction keys, as well as the math keys, a period key, page up and page down keys and an enter key. The function keys are located at the top of the keyboard and extend across the keyboard. These keys can be assigned specific commands as per the operating system or current application. The control keys are located between the typing keys and the numeric keypad and are the keys for home, end, insert, delete, page up, page down as well as the control, alternate and escape keys. These are the common keys that are found on each keyboard, but some keyboards may have additional keys that perform other tasks. Inside the keyboard is a processor that has to understand the position of the key in the key matrix, the amount of bounce and how to filter it and the speed at which to transmit the typematics. Underneath the keys is a key matrix that is a grid of circuits. These circuits are broken at the point below a specific key, in all keyboards except capacitive ones. When the key is pressed, the gap in the circuit is bridges and a tiny amount of current is allowed to flow through. Monitoring the key matrix for continuity at any point on the grid is done by the processor. When a closed circuit is found, the processor compares the location of the closed circuit on the key matrix to the character map in its ROM. A character map is a comparison chart for tells the processor what key is at certain coordinates in the key matrix. When pressing two or more keys simultaneously, the processor checks to see if that combination of keys has a designation in the character map. Switches also relied on by keyboards, initiate a change in the current that flows through the circuits in the keyboard. When one of these key switches is pressed against the circuit, a bounce or a small amount of vibration between the surfaces is created. The keyboard processor recognizes bounces and immediately realizes that the keyboard operator did not cause these. The processor then filters out these bounces treats them as one single keypress. Typematics is a process that occurs when a key is continually held down and the processor determines this to mean to send the character repeatedly to the computer. The range of this process can vary from 30 characters per second to as few as two characters per second. Keyboards use varieties of switch technologies. Most people like to have audible and tactile response when using a keyboard. These responses are the click that is heard when using the keyboard or the feel of the keys as they are used. Several technologies make these possible. These are rubber dome mechanical, capacitive non-mechanical, metal contact mechanical, membrane mechanical and foam element mechanical. The rubber dome is probably the most popular switching technology use in today’s keyboards. In the keyboards that use this technology, a flexible rubber dome with a hard carbon center is located under each key. When a key is pressed, a plunger, located on the bottom of the key, pushes down against the dome pushing the carbon center down until it is pressed against a hard flat surface beneath the key matrix. Releasing the key allows the rubber dome to spring back to its original shape, forcing the key back up. Membrane switches are very similar in operation to rubber dome switches in keyboards. However, one big difference in the two is that the membrane keyboard has a single rubber sheet with bulges for each key instead of each key being separate. Other differences include almost no tactile response and can be difficult to manipulate. These differences explain why these switches are not generally found on common computer systems. Capacitive switches, considered non-mechanical, do not complete a circuit like other keyboard technologies. With these switches, current flows constantly through all parts of the key matrix. Each key is spring-loaded and has a tiny plate attached to the bottom of the plunger. Pressing a key brings this plate close to another plate located directly below it. Bringing these two plates close together affects the amount of current flowing through the matrix at this point. The processor will detect the change and interprets it as a keypress for that location. Even though capacitive switch keyboards are expensive, they have positive advantages such as not suffering from corrosion, not having problems with bounce and they do have a longer life than other keyboards. Metal contact switches contain a spring-loaded key with a strip of metal located on the bottom of the plunger. When the key is pressed, this metal strip connects the two parts of the circuit. The foam element switch is almost the same design, only with a small piece of spongy foam located between the bottom of the plunger and the metal strip that provides for a better tactile response. The disadvantage found with these two switch technologies is that they wear out quicker than the other switches. Information is transmitted from the keyboard to the computer as the operator types. As the typing is occurring, the processor, located in the keyboard, analyzes the key matrix then determines what characters should be sent to the computer. These characters are kept in a buffer of memory, which is then sent in a stream to the computer using a connection. There are several connections available for this task; some of the most popular are the 5-pin DIN connector, the 6-pin IBM PS/2 connector, the 4-pin USB connector or an internal connector. These connectors contain a connecting cable, which is used to power the keyboard and to carry the data from the keyboard to the computer. Once the keyboard controller notifies the operating system that there is data available from the keyboard, the operating system goes to work to determine what is being sent from the keyboard, such as it is a system level command, i.e. Ctrl-Alt-Delete. If the data is not a system level command, the operating system sends the data to the application that is currently running and the application will proceed with the commands that the data has determined. How computer keyboards work is very interesting, especially how fast all the data is transmitted and deciphered, then acted upon by the operating system and the current application.

Layout

1. Computer keyboards are an input device. They put the information a person types into a program on the computer. Most keyboards have 80 to 110 keys. The numbers and letters on the keyboard are displayed keycaps--these are the buttons that are pressed when a person types. The layout of the numbers and letters are the same on every keyboard and they are referred to as the QWERTY.

Key matrix

2. The inside of the keyboard is like a mini-computer and consists of a processor and circuits. These transfer the information to the processor inside of the computer. Inside of the keyboard's processor resides the key matrix. The key matrix is a grid of circuits. These circuits are individually placed under each key. When a key is pushed, it pushes the switch on the circuit board underneath the key causing an electrical current to pass through the circuit and into the processor. When the current passes through, the switch vibrates, signaling the processor to read it.

Keymap

3. The circuit is closed when a key is pressed. The closing of the circuit signals the processor to read the keymap stored within it. The processor uses the keymap, sometimes called the character map, to find the key that is closed off on the board. By using the keymap, the processor in the keyboard can tell which letter is being pushed and if it should be a capital or lowercase letter depending on if the shift key is being pressed.

Communication

4. The keyboard connects to the computer via a five pin male plug or a PS/2 plug. Keyboards and computers work together in a bi-directional format. This means that they can each send information to one another. These bi-directional lines are the clock line coming from the keyboard and the data line coming from the computer. Both lines must be idle, or high in order for the keyboard to send data. The computer will send a signal to the keyboard through the clock line letting it know that the line is clear to send. If the line is not clear, the keyboard will hold the information until the line opens. When the line is low, the keyboard is waiting for a command from the computer. When the computer wants to send information to the keyboard, it brings the data and the clock line low. It does this to ensure that the keyboard does not send it a message at the same time.

Hard Disk Drive (HDD)

In a personal computer, a hard disk drive (HDD) is the mechanism that controls the positioning, reading, and writing of the hard disk, which furnishes the largest amount of data storage for the PC. Although the hard disk drive (often shortened to "hard drive") and the hard disk are not the same thing, they are packaged as a unit and so either term is sometimes used to refer to the whole unit

Almost everyone who has ever used acomputer has erased a file that they later wanted to bring back. The less fortunate may have also had the experience of losing an entire hard drive. Luckily, hard disk recovery allows for lost data to be recovered.

Hard disk recovery is possible because of data remanence, which means that some data continues to exist on the hard drive even after it has been deleted. While data remanence is beneficial to hard disk recovery, there is also a downside; that is, data remanence is one of the most convenient tools used in cyber-espionage. That's why computer security experts tell you that simply erasing a file doesn't always completely delete it.

A hard drive contains a series of hard disks that rotate rapidly. These disks are coated with magnetic particles, similar to a magnetic recording tape. The hard disk is actually very durable, and good maintenance will ensure long life. If it is not exposed to extreme temperatures, and does not suffer any physical damage, it can easily last for ten years. However, hard disks do have several moving parts, and can become damaged or wear out.

Hard disk recovery reconstructs lost files, regardless of whether they were deleted accidentally or are inaccessible due to a crashed hard drive. In some circumstances, the hard disk may become inaccessible because of a hardware problem. The actuator arm, a small mechanical arm that moves back and forth across the disk, may have suffered a mechanical error. In this event, the data is not lost at all, but is just inaccessible due to this mechanical problem. Similarly, the circuit board may develop flaws, which may make the hard disk inoperable. If there are strange noises, or no noise at all, the cause is likely mechanical, and a technician will have to disassemble the hard drive to repair the problem. In some cases, the mechanical problem may cause the drive itself to become damaged, which may directly affect the data. Alternatively, data loss may occur due to a software problem.

Taking a little preventive action can help prevent the need for hard disk recovery. When files become fragmented, they are stored in multiple clusters on the hard drive, which makes the computer take more time to read it. A drive with a lot of fragmentation will be harder to recover in the event of a crash. Therefore, it is recommended to regularly defrag your hard drive.

When a file is deleted, the operating system marks the file name with a character that informs the computer that it has been deleted. The deleted data is actually still on the drive until the file system overwrites it, but the operating system can no longer access it. The process of hard disk recovery finds the data that the operating system is unaware of, but still exists in individual clusters on the hard drive. However, clusters that have become corrupted or physically damaged cannot be recovered. In these cases, hard disk recovery has a greater likelihood of success if it is attempted immediately after the failure so as not to give the sectors with missing data an opportunity to be overwritten. A professional hard disk recovery service will not work on the hard drive itself, but will instead make a sector copy of the hard drive and work from that.

Hard Disk Recovery Services

In today's business world, computers are integral for the survival of any company, large or small. We at Hard Disk Recovery Services (HDRS)understand that the loss of valuable computer data results in a parallel loss of revenue, and our service has helped many companies halt the drain on resources this causes. From our beginnings over 16 years ago as a hard drive repair facility, we have gathered the experience necessary to make us uniquely qualified in the retrieval of lost electronic information.

Hard Disk Data Recovery Experience

At Hard Disk Data Recovery Services our experience lets us provide you with the peace of mind that your data is safe, and recoverable in almost all instances. Our findings have revealed that in the majority of circumstances, important data is never completely lost.

This is the case not only in common user errors, such as accidentally deleted files or formatted drives, but also in the case of:

• Power surges and outages
• Lightning strikes
• Fires, flood and other natural disasters
• Viruses and sabotage
• Equipment malfunctions
• Static electricity

Never Assume You Cannot Recover Data

Never assume your valuable data can't be recovered. Many people who experience data loss, even many experts, often consider the data irretrievable. Many of these experts have contradictory theories about data loss, which makes the issue of data loss especially unclear to the average user. The insight and experience possessed by the technicians at Hard Disk Data Recovery sheds new light on the confusing and frustrating problem of Data loss. Data loss need not be a major crisis - with our help, we can have you back on track within 4-6 days.

In the 16 years that Hard Disk Recovery Services has offered these services, we have developed extensive knowledge covering hard drive infrastructure and electronic circuitry, and we have continually trained our technicians to develop expertise all software and file structures as well. Our experience, our commitment, as well as all our satisfied customers, have made us.