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Max CPUID Value Limit

Common Options : Enabled, Disabled

Quick Review

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 Max CPUID 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.

When enabled, the processor will limit the maximum CPUID input value to 03h when queried, even if the processor supports a higher CPUID input value.

When disabled, the processor will return the actual maximum CPUID input value of the processor when queried.

It is recommended that you leave it at the default setting of Disabled. You should only enable it if you intend to use the Intel Pentium 4 processor with Hyper-Threading Technology with an operating system that does not support it.

Please note that this BIOS feature only allows the Intel Pentium 4 processor with Hyper-Threading Technology to work with operating systems that do not support it. It does not enable the processor's advanced capabilities for such operating systems.


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