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Name: Christian Ludloff
eMail: ludloff@sandpile.org
Date: March 18, 2004 at 11:42:18
Subject: Re: Finding CPU frequency
In Reply To: Finding CPU frequency by
unknow on March 18, 2004 at 10:28:23
Text: | I need to compute the CPU frequency in a driver application
| I just need to know the maximum CPU frequency (not the actual).

Obtaining this information is complicated and processor-specific.
And subject to change, as new CPUs are introduced. So you want to
avoid having to code this stuff all by yourself.

It is likely that the target OS provides a suitable API function.

| All PC's display the CPU frequency...I guess there must be
| some assembly instruction to query the CPU speed.

Yes, most PCs display this type information during POST.

But then, a BIOS is almost always tailored to the particular PC.

| The Intel manual says that the processor clock speed can be got
| thru the CPUID instruction.

Only on selected Intel processors -- not all of them.

| Can someone elaborate how do I do that or any other way?

Intel's CPUID application note provides details on how to extract
the processor speed from the processor name string of a processor
that supports this particular feature.

--
CL
optional link: sandpile.org


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