Windows 8 Task Manager not reporting actual CPU frequency

Solution 1:

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?

Solution 2:

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