Glossary/CPU/Sustained clock

Sustained clock

Sustained clock is the frequency a processor settles at once the system reaches thermal and power equilibrium under continuous load.

Also known as steady-state clock, settled clock

Measured by SystemCheck

Part of the four-stage run: a 60-second sustained CPU load reporting throughput, decay and consistency; a memory stage reporting bandwidth and latency; a calibrated GPU raster load reporting frame time, pacing and decay; and a path tracer reporting samples per second. The paragraphs below say which metric carries this term.

Every machine has two performance personalities. The first few seconds run at boost, drawing from thermal mass that has not yet warmed and a power budget that allows a short excursion. After equilibrium (typically 30 seconds to several minutes depending on cooler mass) the chip settles at the highest frequency it can hold indefinitely. That settled figure is what governs render times, compiles, and long gaming sessions.

Sustained clock is a property of the whole system, not just the CPU. The same processor will settle several hundred megahertz apart in a thin laptop, a well-ventilated tower, and a small-form-factor case. This is why identical part lists do not produce identical experiences.

SystemCheck's CPU stage is deliberately 60 seconds long, and two and a half minutes on the deep run, to reach into this region rather than reporting a boost snapshot. The report separates early throughput from late throughput, so the settled level and the size of the drop are both visible. SystemCheck reports throughput, not frequency in megahertz (a browser cannot read clock speed), but the throughput floor is the practically relevant version of the same fact.

Related terms

Boost clockBoost clock is the highest frequency a CPU will reach opportunistically on a light thread count when thermal and power headroom allow.Read more Thermal decayThermal decay is the measurable fall in performance from the start of a sustained load to its steady state as the system heats and hits its limits.Read more Peak vs sustained performancePeak performance is the best a system does in a short burst; sustained performance is what it holds at equilibrium, and the gap can exceed 30% on laptops.Read more Sustained loadA sustained load is a workload held long enough for the system to reach thermal and power equilibrium, revealing real behaviour rather than a boost snapshot.Read more Thermal throttlingThermal throttling is a processor reducing its clock speed and voltage automatically once it reaches a temperature limit, to avoid damage.Read more

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