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Clock cycle

As explained in Modern C

A clock cycle is one period of a processor's clock signal used as a unit of execution time.

From loop time to cycles

A measured loop body takes about 1.77 × 10⁻⁸ seconds per iteration. On a 2.1 GHz laptop, that is roughly 36 clock cycles. Other measured loops take about 55, 61, and 67 cycles per iteration. section 15.3

A clock cycle is one period of a processor’s clock signal. Expressing elapsed time in cycles makes the cost of repeated computations easier to compare on the measured machine: replacing a simple sum with stats_collect1 adds about 19 cycles per iteration; successive statistical updates add about six cycles each. section 15.3

TAKEAWAY: These are estimates derived from measured time and the laptop’s clock frequency, not universal costs for the C statements. The measured loops have relative standard deviations below 1%; the arithmetic instructions, loads, and stores in an assembler listing provide a separate plausibility check. section 15.3

How Modern C covers it

How deep it goes
Works through converting measured loop times to approximate cycles and comparing costs; does not derive processor timing from individual instructions.
Examples
Uses four loop measurements on a 2.1 GHz laptop and compares a simple sum with three statistical update variants.
What it assumes
Assumes familiarity with C loops and measured execution time; introduces cycle counts through a concrete frequency and timings.
What you can do after
Evaluate/understand approximate per-iteration cycle costs and differences between measured loop implementations.
How it connects
Connects clock frequency, elapsed-time measurement, relative standard deviation, incremental statistics, and assembler inspection.
Cover of Modern C
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Related concepts

This explainer was generated by Manning's knowledge graph from the text of Modern C. The section links point to the parts of the book it draws on.