In a recent discussion, veteran Microsoft engineer Raymond Chen shed light on a curious aspect of Windows: the operating system's tendency to display two different CPU speeds. This behavior is evident in the System > About section of the Settings app, where users might notice two distinct numbers representing the processor's speed.
Chen explains that this dual-display arises because Windows presents two pieces of information sequentially. The first is the processor's brand string, which, in his example, reads "Intel(R) Core(TM) i7-4790 CPU @ 3.60GHz." This string is extracted from the CPUID function codes
0x80000002 through 0x80000004, which return manufacturer-defined strings. Notably, some manufacturers include the CPU speed within this string, as seen with the "@ 3.60 GHz" suffix.The second number is the speed calculated by Windows itself, which, in Chen's case, is "3.71 GHz." This discrepancy arises because the manufacturer-provided speed in the brand string is a static value, while Windows calculates the CPU speed dynamically, reflecting real-time performance metrics.
Chen suggests that manufacturers might include the speed in the brand string to facilitate the detection of overclocking or to ensure that systems are marketed accurately. However, this practice can lead to confusion when the static value doesn't match the dynamic calculation performed by Windows.
For users seeking accurate, real-time CPU performance data, Chen recommends using the Task Manager. By navigating to the Performance tab and selecting CPU, users can view both the base speed and the current operating speed, which may fluctuate based on workload and other factors.
This explanation underscores the complexities involved in hardware-software interactions and highlights the importance of understanding how different components report performance metrics.
Source: The Register https://www.theregister.com/2025/05/21/chen_windows_cpu_speed/?td=keepreading/
