PCI (Peripheral Component
Interconnect) is an interconnection
system between a microprocessor and
attached devices in which expansion
slots are spaced closely for high
speed operation.
Using PCI, a computer can support
both new PCI cards while continuing
to support Industry Standard
Architecture (ISA) expansion cards,
an older standard. Designed by
Intel, the original PCI was similar
to the VESA local bus.
However, PCI 2.0 is no longer a
local bus and is designed to be
independent of microprocessor
design. PCI is designed to be
synchronized with the clock speed of
the microprocessor.
PCI is now installed on most new
desktop computers, not only those
based on Intel's Pentium processor
but also those based on the PowerPC.
PCI transmits 32 bits at a time in a
124-pin connection (the extra pins
are for power supply and grounding)
and 64 bits in a 188-pin connection
in an expanded implementation.
PCI uses all active paths to
transmit both address and data
signals, sending the address on one
clock cycle and data on the next.
Burst data can be sent starting with
an address on the first cycle and a
sequence of data transmissions on a
certain number of successive cycles.
The PCI specifications define two
different card lengths. The
full-size PCI form factor is 312
millimeters long; short PCIs range
from 119 to 167 millimeters in
length to fit into smaller slots
where space is an issue. Like the
full-size PCI, the short PCI is a
high-performance I/O bus that can be
configured dynamically for use in
devices with high bandwidth
requirements.
Most current PCI cards are
half-sized or smaller. There are a
number of variations of PCI,
including CompactPCI, Mini PCI,
Low-Profile PCI, concurrent PCI, and
PCI-X.
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