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

24594 Rev. 3.10 February 2005 AMD64 TechnologyExtended Function8000_0000h:Processor Vendor andLargest ExtendedFunction NumberExtended function 8000_0000h mimics the behavior of standard function 0, exceptthat extended function 8000_0000h returns the largest extended function numberinstead of the largest standard function number.Extended Function 8000_0000h EAX: Largest Extended Function Number. Extendedfunction 8000_0000h loads EAX with the largest CPUID extended function numbersupported by the processor implementation.Extended Function 8000_0000h EBX, EDX, and ECX: Processor Vendor. Extendedfunction 8000_0000h loads a 12-character string into the EBX, EDX, and ECXregisters identifying the processor vendor. For AMD processors, the string isAuthenticAMD. This string informs software that it should follow the AMD CPUIDdefinition for subsequent CPUID function calls. If the function returns a anothervendor’s string, software must use that vendor’s CPUID definition when interpretingthe results of subsequent CPUID function calls. Table 3-1 on page 118 shows thecontents of the EBX, EDX, and ECX registers after executing extendedfunction 8000_0000h on an AMD processor.Extended Function8000_0001h:Processor Signatureand AMD FeaturesLike standard function 1, extended function 8000_0001h returns the processorsignature and feature bits. However, the feature bits returned by this function includea subset of the bits reported by standard function 1, along with additional bits forAMD features.Extended Function 8000_0001h EAX: Processor Signature. Extended function 8000_0001hreturns the processor signature in the EAX register; the signature providesinformation on the processor revision (stepping) level and processor model, as well asthe instruction family that the processor supports.Figure 3-1 on page 119 shows the format of the EAX register following execution ofCPUID extended function 8000_0001h. (The value returned in the EAX register forfunction 8000_0001h is the same as the value returned by standard function 1.)Extended Function 8000_0001h EBX: 12-bit Brand ID. Extended function 8000_0001h returnsa 12-bit brand ID for certain AMD64 processors. As is the case with the 8-bit brand IDCPUID 125