The Unabridged Pentium 4 IA32 Processor Genealogy

Matching the Image to a Processor

CPUID Enhanced to Supply Update Signature

A CPUID request type 1 returns the processor family, model and stepping in the EAX register (see Figure 25-2 on page 635). In addition to returning this information, the CPUID instruction was enhanced (starting with the Pentium® Pro processor) to provide an indication as to whether or not an update was previously been loaded into the processor. In addition to returning the processor family, model and stepping in EAX, the execution of a CPUID request type 1 also causes the processor to store the ID (referred to as the signature) of the Microcode Update image (if one was previously loaded into the processor) in the Microcode Signature MSR. If no update has been loaded into ...