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. You use
a keyboard to enter commands and data into the system. This section looks at keyboards for PCs,
examining the various types of keyboards and how they function, the keyboard-to-system interfaces,
and keyboard troubleshooting and repair.
In the years following the introduction of the original IBM PC, IBM created three keyboard 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 by virtually all PC manufacturers.
The primary keyboard types are as follows:
• 101-key Enhanced keyboard
• 103/104-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 design were soon supplied with virtually
every type of system and terminal IBM sold. Other 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 Enhanced 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 LEDs, depending on whether the unit was sold with an
XT or AT system. (XT systems didn't support the LEDs.) Currently there are many variations from
which to choose, including some with integrated pointing devices, such as the Lenovo TrackPoint
pointing stick, touchpads, trackballs, as well as programmable keys useful for automating routine
tasks. Several connector variations are also available. Whereas PC keyboards started out using a
larger 5-pin DIN (an acronym for Deutsches Institut für Normung e.V.) keyboard connector, current
designs use either the smaller 6-pin mini-DIN connector (often called a PS/2 connector because it
first came on the IBM PS/2 systems) or industry standard universal serial bus (USB). See the section,
“
Keyboard/Mouse Interface Connectors
” and
Figure 15.8
,
later in this chapter, for the physical and
electronic details of the DIN connectors. See the section “
USB Keyboards
,
” later in this chapter, for
