Input Devices - Upgrading and Repairing PCs - page 921

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, in-
cludingsomewithintegratedpointingdevices,suchastheIBMTrackPointpointingstick,
trackballs, and touch pads, as well as programmable keys useful for automating routine
tasks.
IBM(withitsLexmarkkeyboardandprinterspin-off)andUnicomp(whichnowproduces
these keyboards) have produced a number of keyboard models, including versions with
built-in pointing devices and new ergonomic layouts. Several connector variations are
possible as well. 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).
AlthoughtheconnectorsmightbephysicallydifferentbetweenthelargerandsmallerDIN
types, the keyboards are not, and you can either interchange the cables or use a cable ad-
apter to plug one type in to the other; some keyboards you can buy at retail include the
adapter in the package. See the section “ Keyboard/Mouse Interface Connectors ” and Fig-
ure 15.8 , later in this chapter, for the physical and electronic details of these connectors.
Many keyboards now include both the standard mini-DIN as well as USB connectors for
maximumflexibilitywhenattachingtonewersystems.Seethesection “ USBKeyboards ,”
later in this chapter, for details on connecting keyboards via USB.
The 101-key keyboard layout can be divided into the following four sections:
• Typing area
• Numeric keypad
• Cursor and screen controls
• Function keys
The 101-key arrangement is similar to the Selectric keyboard layout, with the exception
of the Enter key. The Tab, Caps Lock, Shift, and Backspace keys have a larger striking
area and are located in the familiar Selectric locations. The Ctrl and Alt keys are on each
side of the spacebar, and the typing area and numeric keypad have home-row identifiers
for touch typing.
The cursor- and screen-control keys have been separated from the numeric keypad, which
is reserved for numeric input. (As with other PC keyboards, you can use the numeric
keypad for cursor and screen control when the keyboard is not in Num Lock mode.) A
division-sign key (/) and an additional Enter key have been added to the numeric keypad.