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Appendix A
71
23913A/0—November 2000
Embedded AMD-K6™ Processors BIOS Design Guide
Preliminary Information
Appendix A
CPUID
mnemonic
opcode
description
CPUID
0F A2h
Identify the processor and its feature set
Privilege:
none
Registers Affected:
EAX, EBX, ECX, EDX
Flags Affected:
none
Exceptions Generated: none
The CPUID instruction is an application-level instruction that software executes to
identify the processor and its feature set. This instruction offers multiple functions,
each providing a different set of information about the processor. The CPUID
instruction can be executed from any privilege level. Software can use the information
returned by this instruction to tune its functionality for the specific processor and its
features.
Beginning with the AMD-K6E processor Model 7, all AMD processors support the
CPUID instruction. However, it is still recommended that software verify that the
CPUID instruction is supported. See “Testing for the CPUID Instruction” on page 58
for more information.
The CPUID instruction supports multiple functions. The information associated with
each function is obtained by executing the CPUID instruction with the function
number in the EAX register. Functions are divided into two types: standard functions
and extended functions. Standard functions are found in the low function space,
0000_0000h–7FFF_FFFFh. In general, all x86 processors have the same standard
function definitions.
Extended functions are defined specifically for processors supplied by the vendor
listed in the vendor identification string. Extended functions are found in the high
function space, 8000_0000h–8FFF_FFFFh. Because not all vendors have defined
extended functions, software must test for their presence on the processor.