The first commercial PC, the Altair 8800 (by MITS), used an Intel 8080 CPU with a clock rate of 2 MHz (2 million cycles/second).
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The original IBM PC (c. 1981) had a clock rate of 4.77 MHz (4,772,727 cycles/second).
Clock rate, the frequency of an electronic oscillator (such as an oscillator crystal) used by computer processor
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Dubbed "Wicked Fast" by the Product Manager, Frank Casanova - who came to Apple from Apollo Computer in Boston, Massachusetts where the Boston term "wicked" was commonly used to define anything extreme - the system ran at a clock rate of a then-impressive 40 megahertz, had 32 KB of Level 2 cache, six NuBus slots and included a number of proprietary ASICs and coprocessors designed to speed up the machine further.
When modifying the operating parameters of a CPU, such as temperature, overclocking, underclocking, overvolting, and undervolting, it may be necessary to verify if the new parameters (usually CPU core voltage and frequency) are suitable for heavy CPU loads.
Introduced in early 1985, the first "VideoDAC" had an output clock rate of up to 75 MHz and 1/4 LSB accuracy—3-8 times better than typical contemporary devices.