Hardware Reference
In-Depth Information
Chapter 15. Input Devices
Keyboards
One of the most basic system components is the keyboard, which is the primary input
device.Youuseakeyboardtoentercommandsanddataintothesystem.Thissectionlooks
atkeyboardsforPCs,examining thevarioustypesofkeyboardsandhowtheyfunction,the
keyboard-to-system interfaces, and keyboard troubleshooting and repair.
IntheyearsfollowingtheintroductionoftheoriginalIBMPC,IBMcreatedthreekeyboard
designs for PC systems, and since then Microsoft has augmented one of them. Together
these designs have become de facto standards in the industry and are shared byvirtually all
PC manufacturers.
The primary keyboard types are as follows:
• 101-key Enhanced keyboard
• 104-key Windows keyboard
• 83-key PC and XT keyboard (obsolete)
• 84-key AT keyboard (obsolete)
This section discusses the 101-key Enhanced and 104-key Windows keyboards, showing
the layout and physical appearance of both. Although you may still find old 83-key and
84-key designs, these are rare today.
Enhanced 101-Key Keyboard
In 1986, IBM introduced the Enhanced 101-key keyboard for the XT and AT models.
This design first appeared in IBM's RT PC, which was a reduced instruction set computer
(RISC) system designed for scientific and engineering applications. Keyboards with this
designweresoonsupplied withvirtually everytypeofsystem andterminal IBMsold.Oth-
er companies quickly copied this design, which became the standard on virtually all PCs
until the introduction of the 104-key Windows keyboard in 1995 (discussed later in this
chapter).
The layout of the enhanced keyboard was improved over that of the 84-key unit, with the
possible exception of the Enter key, which reverted to a smaller size. The 101-key En-
hanced keyboard was designed to conform to international regulations and specifications
for keyboards. In fact, other companies such as Digital Equipment Corporation (DEC) and
Texas Instruments (TI) had already been using designs similar to the IBM 101-key unit.
The IBM 101-key units originally came in versions with and without the status-indicator
