Why Does Windows Show Two Different CPU Speeds? The Hidden Reason Explained

Microsoft senior engineer Raymond Chen explained why Windows sometimes shows two processor speed values on the Settings → System → About page.

The first value comes from the processor brand string returned by the CPUID instruction (functions 0x80000002‑0x80000004). This string, such as “Intel(R) Core(TM) i7‑4790 CPU @ 3.60 GHz”, contains a static speed set by the manufacturer.

The second value (e.g., 3.71 GHz) is an estimate of the CPU’s current operating frequency that Windows calculates, not a real‑time measurement.

Windows derives this estimate by reading data supplied by the processor’s monitoring firmware; it does not continuously poll the actual clock, which can lead to discrepancies between the displayed speed and the hardware’s rated speed.

If the estimated speed exceeds the baseline, it often indicates that the processor is running in a boosted or over‑clocked state, as in the example where 3.71 GHz is about 3 % higher than the 3.60 GHz base.

Some users have speculated that Windows may read values stored by low‑level monitoring programs or BIOS, or that scheduling decisions cause the apparent difference.