IBM PC 300GL Types 6275, Информационное руководство

Страница: 16 / 68

Chapter 2. Expansion-Bus
This section gives an overview of the expansion-bus and explains how advanced buses can
improve performance.
A computer bus is a pathway of wires and signals that carries (or transfers) information
inside the computer; information includes data, addresses, instructions, and controls. The
microprocessor has an external bus, called the processor bus or local bus, that carries
information between the microprocessor and main memory. The processor bus has the
same bus width (64 bits) as the microprocessor and operates at the same external speed.
Another computer bus, the expansion-bus, carries information between the microprocessor or
memory and peripheral I/O devices. While processor-bus performance has improved
rapidly, improvements in expansion-bus performance have not equalled those of
microprocessors and some peripheral devices, such as video and disk controllers.
Regardless of how fast the microprocessor and other components are, data transfers
between them must pass through the expansion-bus.
Your computer has two expansion-buses: the ISA-bus and the PCI-bus. PCI is an advanced
expansion-bus standard developed by the computer industry to keep up with performance
improvements of processor buses and advanced peripheral devices. Although advanced
designs can match the performance of the microprocessor bus only up to a point, they do
achieve higher throughput by speeding up the expansion-bus and widening its data path.
PCI is intended to add to the capability provided by the ISA-bus.
PCI-Bus
An answer to the need for a higher-performance expansion-bus is the peripheral component
interconnect (PCI) bus. PCI architecture offers many features that improve expansion-bus
performance such as:
Ÿ
Microprocessor independence
Ÿ
Industry-standard compatibility
Ÿ
Wider data path (32 bits)
Ÿ
Faster data-transfer rates
Ÿ
More efficient data-transfer methods
Ÿ
Enhanced peripheral-device performance
Ÿ
Automatic configuration
8

Copyright IBM Corp. 1998