Clock rate

Chip manufacturers publish a "maximum clock rate" specification, and they test chips before selling them to make sure they meet that specification, even when executing the most complicated instructions with the data patterns that take the longest to settle (testing at the temperature and voltage that gives the lowest performance).

An A/D Converter has a "clock" pin driven by a similar system to set the sampling rate.

[4] However, the amount of overclocking is limited by the time for the CPU to settle after each pulse, and by the extra heat created.

The first commercial PC, the Altair 8800 (by MITS), used an Intel 8080 CPU with a clock rate of 2 MHz (2 million cycles per second).

Since then, the clock rate of production processors has increased more slowly, with performance improvements coming from other design changes.

[5][6] This is surpassed by the CPU-Z overclocking record for the highest CPU clock rate at 8.79433 GHz with an AMD FX-8350 Piledriver-based chip bathed in LN2, achieved in November 2012.

[7][8] It is also surpassed by the slightly slower AMD FX-8370 overclocked to 8.72 GHz which tops off the HWBOT frequency rankings.

The first fully reversible CPU, the Pendulum, was implemented using standard CMOS transistors in the late 1990s at the Massachusetts Institute of Technology.

There are many other factors to consider when comparing the performance of CPUs, like the width of the CPU's data bus, the latency of the memory, and the cache architecture.

The clock rate alone is generally considered to be an inaccurate measure of performance when comparing different CPUs families.

In addition, subscalar CPUs or use of parallelism can also affect the performance of the computer regardless of clock rate.