CPUID—CPU Identification

INSTRUCTION SET REFERENCE, A-L

3-200 Vol. 2A

Processor Frequency Information Leaf 

16H

EAX

Bits 15 - 00: Processor Base Frequency (in MHz).

Bits 31 - 16: Reserved =0.

EBX

Bits 15 - 00: Maximum Frequency (in MHz).

Bits 31 - 16: Reserved = 0.

ECX

Bits 15 - 00: Bus (Reference) Frequency (in MHz).

Bits 31 - 16: Reserved = 0.

EDX

Reserved.

NOTES:

* Data is returned from this interface in accordance with the processor's specification and does not reflect 

actual values. Suitable use of this data includes the display of processor information in like manner to the 

processor brand string and for determining the appropriate range to use when displaying processor 

information e.g. frequency history graphs. The returned information should not be used for any other 

purpose as the returned information does not accurately correlate to information / counters returned by 

other processor interfaces. 

While a processor may support the Processor Frequency Information leaf, fields that return a value of 

zero are not supported.

System-On-Chip Vendor Attribute Enumeration Main Leaf (EAX = 17H, ECX = 0)

17H

NOTES:

Leaf 17H main leaf (ECX = 0).
Leaf 17H output depends on the initial value in ECX.
Leaf 17H sub-leaves 1 through 3 reports SOC Vendor Brand String.

Leaf 17H is valid if MaxSOCID_Index >= 3.
Leaf 17H sub-leaves 4 and above are reserved.

EAX

Bits 31 - 00: MaxSOCID_Index. Reports the maximum input value of supported sub-leaf in leaf 17H.

EBX

Bits 15 - 00: SOC Vendor ID.

Bit 16: IsVendorScheme. If 1, the SOC Vendor ID field is assigned via an industry standard enumeration

scheme. Otherwise, the SOC Vendor ID field is assigned by Intel.

Bits 31 - 17: Reserved = 0.

ECX

Bits 31 - 00: Project ID. A unique number an SOC vendor assigns to its SOC projects.

EDX

Bits 31 - 00: Stepping ID. A unique number within an SOC project that an SOC vendor assigns.

System-On-Chip Vendor Attribute Enumeration Sub-leaf (EAX = 17H, ECX = 1..3)

17H

EAX

Bit 31 - 00: SOC Vendor Brand String. UTF-8 encoded string.

EBX

Bit 31 - 00: SOC Vendor Brand String. UTF-8 encoded string.

ECX

Bit 31 - 00: SOC Vendor Brand String. UTF-8 encoded string.

EDX

Bit 31 - 00: SOC Vendor Brand String. UTF-8 encoded string.

NOTES:

Leaf 17H output depends on the initial value in ECX.
SOC Vendor Brand String is a UTF-8 encoded string padded with trailing bytes of 00H.
The complete SOC Vendor Brand String is constructed by concatenating in ascending order of
EAX:EBX:ECX:EDX and from the sub-leaf 1 fragment towards sub-leaf 3.

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

Initial EAX 

Value

Information Provided about the Processor