UPGRADING REPAIRING PCs

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Chapter 2—System Components and Configuration
another.
Expansion Slots
If you want to add network, SCSI, modem, or sound capabilities to
an existing system or upgrade your video card, you need to understand
expansion slots. Expansion slots act as an extension of the
system bus and permit you to connect cards with different features
to your system.
ISA
ISA (Industry Standard Architecture) expansion slots are the oldest
expansion slot design found in current PCs. 8-bit versions go all
the way back to the original IBM PC of 1981. While 8-bit–only ISA
slots have faded away, 16-bit ISA slots (introduced with the IBM
PC/AT in 1984) are fully pin-compatible with 8-bit ISA cards. See
Figures 2.18 and 2.19.
Figure 2.19 shows the orientation and relation of 8-bit and 16-bit
ISA bus slots.
EISA—A 32-bit Version of ISA
The EISA (Enhanced ISA) bus was developed from the ISA architecture
to provide 32-bit data transfers. The EISA expansion slot (introduced
in 1988) is a deeper version of ISA, providing a second, offset
row of connectors that allows EISA slots to support ISA cards.
Figure 2.20 shows the locations of the pins.
Because of its high cost and limited performance boost over ISA,
EISA bus systems have primarily been used for network file servers
using 386, 486, and occasionally Pentium-class CPUs.
EISA was introduced as a response to IBM’s MicroChannel architecture,
which was used primarily on more-advanced models of IBM’s
PS/2 line from 1987 until the early 1990s. It is now obsolete.
VL-Bus—A Faster 32-Bit Version of ISA
Introduced in 1992, the VL-Bus (VESA Local-Bus) was an improved
32-bit version of ISA designed originally to provide faster video