The Keyboard

The Workhorse of Input

The basic layout of the keys on the computer keyboard evolved from an earlier office workhorse, the typewriter. Despite this distant kinship, however, the differences between computer keyboards and typewriters far outweigh their apparent similarities.

The first distinction is that the keys on a computer keyboard, unlike those of a typewriter, have no intrinsic meaning. The keys are marked with letters of the alphabet and numbers, but they can be assigned an infinite variety of other meanings, depending on what is wanted by program designers, systems engineers and even the individual user, who is also able to customize the keyboard. Thus, while depressing the letter Q means 'Q' in a word-processing context, it can just as easily mean 'Queen' in a chess program, or 'Quit' in a math program. In some other application, it can be assigned a meaning that has no connection at all to the letter Q in the alphabet.

In typing a document with a word-processing program the ENTER key is treated like a Return key. Other programmes use the ENTER key differently, and most use it as a "go do it" command, so whichever command is issued will not be executed until ENTER is pressed.

In addition to conventional typewriter keys, the keyboard also has function keys, which can be assigned a variety of tasks to meet the demands of different software packages. There are also several single-purpose keys on the keyboard. These include the cursor keys, which are used to move an on-screen marker called the cursor. The cursor's feedback helps the user interact with the computer by indicating the location of the next character to be entered.

Under the keyboard's surface is a circuit board with contacts and wires marking out a grid whose coordinates have a significance to the computer. Pressing any key closes a switch at an intersection on the matrix of wires printed on the circuit board. This generates a scan code, which identifies the key by a numerical set of coordinates. The scan code travels along a cable and through a keyboard port, directly to the CPU.

The CPU then consults a hard-wired electronic list called a look-up table, located in ROM-the computer's permanent, factory-installed Read Only Memory. The look-up table cross-references each scan code against a binary number that stands for a meaningful symbol, such as a letter of the alphabet. Typically, the look-up table defines keys according to the computer's usual functions: the entry of numerical data, for example, or the use of a particular alphabet for word-processing. Computers in Western countries usually convert scan codes into ASCII-American Standard Code for Information Interchange. This standard uses 128 binary numbers to represent upper- and lower-case letters, numerals, typographical symbols and a variety of codes that instruct the computer to perform such assorted functions as backspacing or sounding its beeper.

Here are some keyboard keys that are not found on a typewriter

• ESC The escape key is the upper-left corner of the keyboard that cancels commands and stops tasks that are underway.
• CNTRL & ALT These keys are used to send commands to the computer by pressing and holding one or both while a letter is pressed key. The CTRL-letter and ALT-letter key combinations are often called hotkey commands because commands are executed from the keyboard instead of from pull-down menus.
• Windows 9x Keys Most newer computers also have two keys that are used with Microsoft's Windows 9x. One has an icon of a small pull-down menu printed on it. When this is pressed it opens the menu for the programme currently being worked on. The other key is the Microsoft Windows logo pressing it is like clicking the on-screen Start button.
• Function Keys Above (or to the side of) the main section of the keyboard are 12 keys called Function Keys, which are numbered from F1 through F12. These keys launch commands just as the CTRL: and ALT keys do. The actual commands these keys launch are controlled by the program, and unfortunately there is no standard for which key does what.. However, the F1 key usually is the Help key, and pressing it will summon online technical assistance.

  The right side of the keyboard contains the numeric keypad. These keys perform two functions. The keys numbered from 0 to 9 (there is also a decimal point key) also are marked with arrows pointing up, down, left and right, as well as keys marked PGUP, PGDN, HOME, END, IND, and DEL. In the upper-left corner of this keyboard, there is a key labelled NUM LOCK and a light with the same marking that will be on or off.

• Numeric Keypad. The NUM LOCK key controls the function of the numeric keypad: press it so that the light comes on, and the numerals become operational; press it so that the light goes off, and the directional arrows, page-scrolling, and cursor control features are activated.