how does a computer know which key is pressed?

Answer 1

The keyboard contains electronic board inside it and the circuit is designed and programmed to work in the machine. This is the way how the computer knows the key which we press.

Answer 2

The keyboard has a matrix arrangement for the keys, that means, each time a key is pressed, a small current flows from one direction to another on an X,Y axis, and activates an integrated circuit than interprets the coordinate on the matrix, and translates that coordinate to the correspondent binary code for that letter, number, or function key. That integrated circuit then transmits the data to your mother board. Usually the mother board overrides the keyboard IC controller, that allows the user to change different settings for example choseing the language for the keyboard, (ie: You can write in Spanish with a french configured keyboard), activating multimedia keys, etc. The rest is done by the processor.

And plase excuse my poor spelling

Answer 3

This is a computer question and not a physics question. However to answer this question the key sends a sequence of characters(for example a-z and 0-9 and other character one char and function keys as combination of 2 keys and they are interpreted by BIOS(in dos and similar in other OS) This get interpreted through interrupts.
to know what key is pressed

Answer 4

It doesn't know anything. A computer doesn't know,feel,understand,immagine,think,dream,plan or have any kind of insight based knowledge. Each key has a contact thing that connects to a contact thing under it. Once the key is hit or pressed down. The letter or character is transmitted to the screen. Kind of like when two hands smack together to make a claping sound. Each key has a binary ID number based on the ASC2 American Standard Code for Information Interchange. The letter (A) ASC2 code is 65.The Binary number is; 01000001.

Answer 5

Computer is an inorganic substance which cannot know and nor feel. It is only a machine with a motherboard. The Central Processing Unit constitutes so many different chips for the purpose. When we type a key, it is input in the form of binary numbers and they inturn are output in the form of letters and digits. This process is programmed in such a way.

Answer 6

Its all mechanical and electronic - the keys when pressed, touch the other end and hence let the current flow through them, this current goes to a certain section in computer which realizes the key owing to the currents spatial characteristics and I think thts enough to make u understand in a layman style...

Answer 7

Each key has a unique binary code or electric signal when we press so computer can uniquely identify each and every keys .

then the rest the programs will handle it and we have many standard codes like ASCI and another for IBM ans so on but most popular one it ASCI .American standard code of ........

Answer 8

computer knows which key you have press because there are some programs connect to the cpu.cpu is brain of the computer. when we type, computer converts its language into our language . and we can see our commands on moniter.

Answer 9

itz really simple u knw as we all knw tht the computer has a mother board which a integrated circuit ,a printed circuit so wen we press the key ,tht particular key completes the circuit n tht works off it thn tht the pc knws which key i pressed

Answer 10

There are several types of keyboard, usually differentiated by the switch technology employed in their operation. Since there are so many switches needed (usually about 80-110) and because they have to be highly reliable, this usually defines the keyboard. The choice of switch technology affects key response (the positive feedback that a key has been pressed) and travel (the distance needed to push the key to enter a character reliably). Newer models use hybrids of various technologies to achieve greater cost savings.

Types
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Dome-switch keyboard
Dome-switch keyboards are kind of a hybrid of membrane and mechanical keyboards. They bring two circuit board traces together under a rubber "dome" or bubble. The top of the bubble is coated in some conductive substance. When a key is pressed, it collapses the dome, which shorts out the two circuit traces and completes the connection to enter the character. The pattern on the PC board is often gold-plated.

This is a common switch technology used in mass market keyboards today. It is considered very quiet, but purists tend to find it "mushy" because the collapsing dome does not provide as much positive response as a hard closing switch. These are also a good choice for office or consumer environments because they are generally fairly quiet. This switch technology also happens to be most commonly used in handheld controllers, such as those used with home video game consoles.

Dome-switch keyboards are also called direct-switch keyboards.

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Capacitive keyboard
In this type of keyboard, pressing the key changes the capacitance of a pattern printed on a PC board. Usually this permits a pulse or pulse train to be sensed. Unlike "dome switch" keyboards, the pattern will be covered by a thin, insulating film. Capacitive keyboards are inexpensive, and resist wear, water, foreign objects and dirt. They are common in PC keyboards.

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Mechanical-switch keyboard
Mechanical-switch keyboards use real switches, one under each key. Depending on the construction of the switch, these keyboards have varying responses and travel times. Notable keyboards utilizing this technology are the Apple Extended II and its modern imitator, the Matias Tactile Pro. These two keyboards use ALPS switches. Cherry Corporation of Germany also makes mechanical switches used in special purpose and high end keyboards. The Matias Tactile Pro is a decent approximation of the Apple Extended II keyboard, however the grade of the plastic is noticeably cheaper. Its construction , besides having decent quality key-switches, is less than par, with flimsy keyboard risers on the bottom of the keyboard and USB ports that are too tight. Although the keyboard has these quality flaws, it's still better than most available keyboards today, except probably the IBM Model M replacements.

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Buckling-spring keyboard
It is a common misconception that the IBM Model M and its derivates are mechanical-switch keyboards. In fact, the Model M uses membrane-sheet switches, much like those found in a dome-switch keyboard. The buckling spring mechanism (U.S. Patent 4,118,611) atop the switch is responsible for the tactile and aural response of the keyboard. This mechanism controls a small hammer that strikes the membrane switch. For more information, see an examination of buckling-spring technology.

In 1993, two years after spawning Lexmark, IBM transferred its keyboard operations to the daughter company. New Model M keyboards continued to be manufactured for IBM by Lexmark until 1996, when Unicomp purchased the keyboard technology. Today, Unicomp manufactures new buckling-spring keyboards and repairs old IBM and Lexmark keyboards. Unfortunately, the later Lexmark-manufactured Model M keyboards are of inferior quality to the original IBM-manufactured Model M. The plastic used is of lower grade (density) and other features such as a detachable heavy duty keyboard cord were replaced by cheap substitutes.

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Hall-effect keyboard
Hall effect keyboards use magnets and Hall effect sensors instead of an actual switch. When a key is depressed, it moves a magnet, which is detected by the solid-state sensor. These keyboards are extremely reliable, and are able to accept millions of keystrokes before failing. They are used for ultra-high reliability applications, in locations like nuclear powerplants or aircraft cockpits. They are also sometimes used in industrial environments. These keyboards can be easily made totally waterproof. They also resist large amounts of dust and contaminants. Because a magnet and sensor is required for each key, as well as custom control electronics, they are very expensive.

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Laser keyboard
A laser projection device approximately the size of a computer mouse projects the outline of keyboard keys onto a flat surface, such as a table or desk. When the laser is interrupted in the position of a key, a keystroke is registered. This type of keyboard is very portable, and many models have retractable cords and wireless capabilities. However, sudden or accidental disruption of the laser will register unwanted keystrokes. Also, if the laser malfunctions, the whole unit becomes useless, unlike conventional keyboards which can be used even if a variety of parts (such as the keycaps) are removed. This type of keyboard can be cumbersome to use since it is susceptible to errors, even in the course of normal typing.

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Membrane keyboard
Main article: Membrane keyboard
Membrane keyboards are usually flat. They are most often found on appliances like microwave ovens or photocopiers. A common design consists of three layers. The top layer (and the one the user touches) has the labels printed on its front and conductive stripes printed on the back. Under this it has a spacer layer, which holds the front and back layer apart so that they do not normally make electrical contact. The back layer has conductive stripes printed perpendicularly to those of the front layer.

When placed together, the stripes form a grid. When the user pushes down at a particular position, his finger pushes the front layer down through the spacer layer to close a circuit at one of the intersections of the grid. This indicates to the computer or keyboard control processor that a particular button has been pressed.

Membrane keyboards do not generally have much of a "feel", so many machines which use them issue a beep or flash a light when the key is pressed. They are often used in harsh environments where water or leak proofing is desirable. Although used in the early days of the personal computer (on the ZX80, ZX81 and Atari 400), they have been supplanted by the more tactile dome and mechanical switch keyboards. However, membrane keyboards with interchangeable key layouts, such as the IntelliKeys and Discover:board are still commonly used by people with physical, visual, or cognitive disabilities as well as people who require assistive technology to access a computer.

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Roll-up keyboard
Some keyboards are designed out of flexible materials that can roll up in a tight (but not too tight) bundle. Normally the external materials are either silicone or PU. It is important to note that although many manufacturers claim that the keyboards are foldable, they cannot be folded without damaging the membrane that holds the circuitry.

Typically they are completely sealed in rubber, making them watertight like membrane keyboards. Like membrane keyboards, they are reported to be very hard to get used to, as there is little tactile feedback.

See Roll-away computer.

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Waterproof Keyboards
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Other parts of PC keyboard
The modern PC keyboard is more than just the switch technology, however. It also includes a control processor and indicator lights to provide feedback to the user about what state the keyboard is in. Depending on the sophistication of the controller's programming, the keyboard may also offer other special features.

The processor is usually a single chip 8048 microcontroller variant. The keyboard switch matrix is wired to its inputs and it processes the incoming keystrokes and sends the results down a serial cable (the keyboard cord) to a receiver in the main computer box. It also controls the illumination of the "caps lock", "num lock" and "scroll lock" lights.

A common test for whether the computer has crashed is pressing the "caps lock" key. The keyboard sends the key code to the BIOS code running in the main computer; if the main computer is operating, it commands the light to turn on. All the other indicator lights work in a similar way. The BIOS also tracks the shift, alt and control state of the keyboard.

When pressing a keyboard key, the key "bounces" like a ball against its contacts several times before it settles into firm contact. When released, it bounces some more until it reverts to the uncontacted state. If the computer was watching for each pulse, it would see many keystrokes for what the user thought was just one.

To resolve this problem, the processor in a keyboard (or computer) "debounces" the keystrokes, by aggregating them across time to produce one "confirmed" keystroke that (usually) corresponds to what is typically a solid contact. It could be argued that the dome switch technology outlined above owes its popularity to the ability of the processor to accurately debounce the keystrokes. Early membrane keyboards limited typing speed because they had to do significant debouncing. Anyone who ever tried word processing on a ZX81 will recall this.