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Computing (FOLDOC) dictionary
clock rate
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processor, benchmark The fundamental rate in cycles per
second at which a computer performs its most basic operations
such as adding two numbers or transfering a value from one
register to another.
The clock rate of a computer is normally determined by the
frequency of a crystal. The original IBM PC, circa 1981,
had a clock rate of 4.77 MHz (almost five million
cycles/second). As of 1995, Intel's Pentium chip runs at
100 MHz (100 million cycles/second). The clock rate of a
computer is only useful for providing comparisons between
computer chips in the same processor family. An IBM PC with
an Intel 486 CPU running at 50 MHz will be about twice as
fast as one with the same CPU, memory and display running at
25 MHz. However, there are many other factors to consider
when comparing different computers. Clock rate should not be
used when comparing different computers or different processor
families. Rather, some benchmark should be used. Clock
rate can be very misleading, since the amount of work
different computer chips can do in one cycle varies. For
example, RISC CPUs tend to have simpler instructions than
CISC CPUs (but higher clock rates) and pipelined
processors execute more than one instruction per cycle.