P4 640 to 670 (Wont go to 3.8)

199.6 x 14 = 3.794.4GHz ~ 3.8GHz

The first number is the base clock and the second number is the multiplier. The CPU speed is the multiplier times the base clock. 199.6MHz is within variation. It also varies. Mine is varying from 199.9 to 201.7 as we speak. 0.0006GHz honestly makes zero difference.
 

senna

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Mar 8, 2010
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1: The motherboard on that computer may not support the high multiplier of that CPU. Check the manufacturer's website.

2: The computer may have some sort of power saving features enabled, check in the bios and the power options control panel in your system to see if it is set to "power saver". If it is on, the computer might scale the multiplier down to 14 instead of the rated 19 to save power.


Cheers!
 

A few years ago I bought a Compaq ML110 G2 motherboard because the owner had a similar problem. His new 3.6 GHz CPU would only run at 2.8 GHz which happens to be the default speed when a CPU is not recognized. I'm currently using it with a 3.2 GHz CPU that's officially supported. The maximum is 3.4 GHz and that's probably the same with your system.