CPU Stress Test at 100% appears as only 87% CPU Usage in Task Manager! Is this normal?

[BLaZiNgSPEED]

I tested My Quad Core Q8400 2.66 GHz with Prime95. Everything goes to 100% as indicated by RealTemp. But when I check my Task Manager it shows at 87% instead of 100%! What is the reason for this?

This is stock speed. I even reseated the cooler, cleaned dust and reapplied fresh thermal paste. I even reset BIOS to defaults. Flashed BIOS. But the CPU usage on Windows 8.1 Pro freshly installed shows only 87% as max in Task Manager. Temperatures are normal.

Before when I ran on Windows 7 last year I think the CPU usage at Task Manager back then was 100%. But here on Windows 8.1 it shows as 87% instead. I am really confused. Any ideas? Is this normal?

Many thanks!

 

[CompuTronix]

Real Temp and Windows 7 are both correct. Task manager in Windows 8, 8.1 and 10 will sometimes display erroneous values for CPU Usage. Hopefully Microsoft will one day correct these issues before they release their next OS with it's own batch of bugs.

You can rest assured that Real Temp is indeed correct. It was developed specifically for Intel processors, has stood the test of time, and has been proven to be accurate.

CT

 

[BLaZiNgSPEED]

Real Temp and Windows 7 are both correct. Task manager in Windows 8, 8.1 and 10 will sometimes display erroneous values for CPU Usage. Hopefully Microsoft will one day correct these issues before they release their next OS with it's own batch of bugs.

You can rest assured that Real Temp is indeed correct. It was developed specifically for Intel processors, has stood the test of time, and has been proven to be accurate.

CT

Many thanks for your reply.

It would indeed be reassuring to know that the reported CPU usages in Windows 8.1 are incorrect. Although I am still worried because in other posts I heard that the CPU must have been at a course of end of life which is why it can no longer utilize 100% CPU usage.

I really wanted to be 100% certain that this isn't a hardware fault from the CPU or PSU for that matter. I am even tempted to reformat windows and install Windows 7 to confirm whether this is indeed the case.

I have made the same CPU stress test on my dad's PC although he has an AMD FX-8370 with Windows 8.1 the Utilization goes to 100% with 4.0 GHz Speed on his Task Manager.

I guess it may certainly be an incorrect reporting on Windows 8.1 with Intel. But I still wanted to be 100% certain, though.