BIOS Option Of The Week - CPUID Maximum Value Limit

Posted on Sunday, Nov 11 2012 @ 15:39 CET by Thomas De Maesschalck
This week TechARP reveals the meaning of the CPUID Maximum Value Limit BIOS option, you can learn about it over here.
When the computer is booted up, the operating system executes the CPUID instruction to identify the processor and its capabilities. Before it can do so, it must first query the processor to find out the highest input value CPUID recognizes. This determines the kind of basic information CPUID can provide the operating system.

The maximum CPUID input value determines the values that the operating system can write to the CPUID's EAX register to obtain information about the processor.

Intel processors from the Pentium Pro onwards have a maximum CPUID input value of only 02h or 03h. The only exception is the Intel Pentium 4 with Hyper-Threading Technology (HTT).

Older operating systems like Windows 95/98 and Windows Me were released before the Intel Pentium 4 with HTT and are therefore not aware of such a processor. They are not capable of handling the extra CPUID information provided by the processor with EAX input values greater than 03h.

This is where the CPUID Maximum Value Limit BIOS feature comes in. It allows you to circumvent problems with older operating systems that do not support the Intel Pentium 4 processor with Hyper-Threading Technology.

About the Author

Thomas De Maesschalck

Thomas has been messing with computer since early childhood and firmly believes the Internet is the best thing since sliced bread. Enjoys playing with new tech, is fascinated by science, and passionate about financial markets. When not behind a computer, he can be found with running shoes on or lifting heavy weights in the weight room.

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