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X-Hacker.org- Peter Norton Programmer's Guide - Norton Guide
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The clock generator supplies the multiphase clock signals that
coordinate the microprocessor and the peripherals. The clock generator
produces a high-frequency oscillating signal. For example, in the
original IBM PC, this frequency was 14.31818 megahertz (MHz, or million
cycles per second); in the newer machines, the frequency is higher.
Other chips that require a regular timing signal obtain it from the
system clock generator by dividing the base frequency by a constant to
obtain the frequency they need to accomplish their tasks. For example,
the IBM PC's 8088 is driven at 4.77 MHz, one-third of the base
frequency. The PC's internal bus and the programmable interval timer
(discussed shortly) use a frequency of 1.193 MHz, running at a quarter
of the 8088 rate and one-twelfth of the base rate.
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