Also known as: Clock rate

Clock speed (or clock rate) is the frequency at which a processor’s internal clock ticks, measured in hertz, setting the basic pace at which the chip steps through its work.¹

A clock is a square wave: each low-to-high tick, or cycle, lets the logic settle and advance one step. How many cycles fit in a second is the frequency — 3 GHz means three billion a second. But heat and power cap how fast it can tick, and how much work each cycle does matters just as much, so clock speed alone does not equal performance.

Overview

A digital chip advances in time with a clock signal; each tick, or cycle, lets the logic settle and move to its next state. A 3 GHz CPU ticks three billion times a second. But clock speed alone does not equal performance — how much work per cycle (instructions per cycle, dependent on the microarchitecture, cache behavior, and parallelism) matters just as much. Comparing clock speeds across different designs is therefore unreliable.

Where it fits

For years rising clock speeds delivered most of computing’s gains, but heat and power put a hard ceiling on how fast a chip can tick — push too far and it overheats, so cooling and throttling govern the real sustained rate. With the end of easy clock scaling (part of the Dennard-scaling breakdown noted under Moore’s law), designers turned to more cores instead. For steady SDR decoding, sustained clock under thermal load matters more than a high peak boost a node cannot hold.

Sources

1. Clock rate — Wikipedia, on processor clock frequency and its limits. ↩

See also

• Central processing unit (CPU)
• Cooling & thermals
• Cache memory
• Moore's law
• Transistor
• Instruction set architecture (ISA)