3-111
INSTRUCTION SET REFERENCE
CPUIDCPU Identification
Description
This instruction provides processor identification information in registers EAX, EBX, ECX, and
EDX. This information identifies Intel as the vendor, gives the family, model, and stepping of
processor, feature information, and cache information. An input value loaded into the EAX
register determines what information is returned, as shown in Table 3-6.
The CPUID instruction can be executed at any privilege level to serialize instruction execution.
Serializing instruction execution guarantees that any modifications to flags, registers, and
memory for previous instructions are completed before the next instruction is fetched and
executed. For more information, refer to Section 7.4., Serializing Instructions in Chapter 7,
Multiple-Processor Management of the Intel Architecture Software Developers Manual,
Volume 3.
When the input value in register EAX is 0, the processor returns the highest value the CPUID
instruction recognizes in the EAX register (refer to Table 3-6). A vendor identification string is
returned in the EBX, EDX, and ECX registers. For Intel processors, the vendor identification
string is GenuineIntel as follows:
EBX
<
756e6547h (* "Genu", with G in the low nibble of BL *)
EDX
<
49656e69h (* "ineI", with i in the low nibble of DL *)
ECX
<
6c65746eh (* "ntel", with n in the low nibble of CL *)
Opcode
Instruction
Description
0F A2
CPUID
EAX
<
Processor identification information
Table 3-6. Information Returned by CPUID Instruction
Initial EAX
Value
Information Provided about the Processor
0
EAX
EBX
ECX
EDX
Maximum CPUID Input Value (2 for the P6 family processors and 1 for the
Pentium
®
processor and the later versions of Intel486 processor that
support the CPUID instruction).
Genu
ntel
ineI
1
EAX
EBX
ECX
EDX
Version Information (Type, Family, Model, and Stepping ID)
Reserved
Reserved
Feature Information
2
EAX
EBX
ECX
EDX
Cache and TLB Information
Cache and TLB Information
Cache and TLB Information
Cache and TLB Information
