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Task manager reports 2.53 GHz, but CPU-Z reports 1192 MHz. My windows is a fresh install of the Windows 8 Pro Upgrade. When I used the Consumer Preview, task manager would report different frequencies, but in my current installation this doesn't happen.

I'm currently running on battery, 64-bit, Intel Core i5 540M.


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up vote 6 down vote accepted

I turned Virtualisation off in the BIOS, and now Task Manager shows a difference between the marketed speed and the actual speed. On a side note, I notice that CPU-Z seems to only show the clock speed of core 0, whereas perhaps Task Manager shows the average?

Thanks for @MartheenCahyaPaulo for providing this answer in the comments. Now the next question is why does Task Manager behave like that with Virtualisation turned on?

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Ah, it seems to be related to certain drivers… Haven't tried it though, still in the middle of unresumable download. – Martheen Cahya Paulo Nov 25 '12 at 11:00

What your seeing is completely correct. It's a system Intel implements into its newer processors called Speedstep.

Since your on a laptop (or using a mobile CPU at any rate), you usually want to save power. Instead of the processor running at a blistering 2.5GHz at all times, it slows down. When you need to do more processing, it speeds up again. It's an effort to save you some more battery

So the number you are seeing is correct at that moment on CPU-z

Windows task manager isn't a very smart application sometimes, so it shows the FULL speed, not the current speed

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My task manager shows the speed fluctuating. It's not always the same as CPU-Z, making me wonder if they're polling at different rates or something. Either way when I alt-tab back to the video game I was playing, they both shot up to the max speed again. – Mark Allen Nov 25 '12 at 8:05

It seems to be because when you enable Hyper-V it takes over the speed management of the processor so that the guests don't try and control it and send conflicting instructions. Basically what task manager is seeing is a virtualised CPU whereas the CPU-Z application is seeing the raw CPU.

I don't have Hyper-V enabled and task manager shows the actual speed of my CPU.

More information can be found here.

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