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Computer Busses by William Buchanan

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4

PCI Bus

4.1 Introduction

The PC was conceived at a time when processor clock speeds were measured in several MHz. Initially this was set at 4.77 MHz, and then increased to 8 MHz. The PC and ISA busses fossilised with these clock frequencies. In the first few years of its design, the motherboard ran at the same speed as the processor. Soon, with improvements in silicon design, the speed of the processor was increased to tens of megahertz. Soon the maximum limit of the motherboard was reached and the only way to break this limit was to double or treble the motherboard clock speed. This limit was set at 33 MHz or 50 MHz. Processor speed has since been risen to over 500 MHz. Local bus technology uses the speed of the motherboard, rather than a fixed ...

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