CPUID—CPU Identification

INSTRUCTION SET REFERENCE, A-L

3-202 Vol. 2A

INPUT EAX = 0: Returns CPUID’s Highest Value for Basic Processor Information and the Vendor Identification String

When CPUID executes with EAX set to 0, the processor returns the highest value the CPUID recognizes for 
returning basic processor information. The value is returned in the EAX register and is processor specific.

80000004H EAX

EBX

ECX

EDX

Processor Brand String Continued.

Processor Brand String Continued.

Processor Brand String Continued.

Processor Brand String Continued.

80000005H EAX

EBX

ECX

EDX

Reserved = 0.

Reserved = 0.

Reserved = 0.

Reserved = 0.

80000006H EAX

EBX

Reserved = 0.

Reserved = 0.

ECX

EDX

Bits 07 - 00: Cache Line size in bytes.

Bits 11 - 08: Reserved.

Bits 15 - 12: L2 Associativity field *.

Bits 31 - 16: Cache size in 1K units.

Reserved = 0.

NOTES:

* 

L2 associativity field encodings:

00H - Disabled.

01H - Direct mapped.

02H - 2-way.

04H - 4-way.

06H - 8-way.

08H - 16-way.

0FH - Fully associative.

80000007H EAX

EBX

ECX

EDX

Reserved = 0.

Reserved = 0.

Reserved = 0.

Bits 07 - 00: Reserved = 0.

Bit 08: Invariant TSC available if 1.

Bits 31 - 09: Reserved = 0.

80000008H EAX

Linear/Physical Address size.

Bits 07 - 00: #Physical Address Bits*.

Bits 15 - 08: #Linear Address Bits.

Bits 31 - 16: Reserved = 0.

EBX

ECX

EDX

Reserved = 0.

Reserved = 0.

Reserved = 0.

NOTES:

*  If CPUID.80000008H:EAX[7:0] is supported, the maximum physical address number supported should 

come from this field.

Table 3-8.  Information Returned by CPUID Instruction (Contd.)

Initial EAX 

Value

Information Provided about the Processor