Volume 3: General-Purpose and System Instructions - Stanford ...

24594 Rev. 3.10 February 2005 AMD64 TechnologyStandard Function 1:Processor Signatureand StandardFeaturesStandard Function 1 returns the processor signature and standard-feature bits.0000_0001h EAX: Processor Signature. Function 1 returns the processor signature in theEAX register; the signature provides information on the processor revision (stepping)level and processor model, as well as the instruction family that the processorsupports.Figure 3-1 shows the format of the EAX register following execution of CPUIDstandard function 1.31 28 27 20 19 16 15 12 11 8 7 4 3 0Reserved Extended Family Extended Model Reserved Family Model SteppingBits Mnemonic Description31–28 Reserved27–20 Extended Family19–16 Extended Model15–12 Reserved11–8 Family7–4 Model3–0 SteppingFigure 3-1.Standard Function 1 EAX : Processor Signature (EAX Register)The extended family and extended model fields extend the family and model fields,respectively, to accommodate larger family and model values. The method forcomputing the actual—or effective—family and model depends on the value of thefamily field. The method for computing the effective family is shown in Table 3-2.CPUID 119