wikiCPUID
The actual processor signature, which identifies a processor type, is often referred to as the CPUID. The CPUID Opcode itself is a "Processor supplementary capability'" for the x86 architecture that enables it for the software to recognize details of the processor. The software can determine the Processor signature and the availability of functions (such as MMX/SSE) by using the CPUID Opcode. For user and administrators is the processor identifier, also known as CPUID or processor signature, particularly relevant when it comes to finding the latest microcode version for the CPU in use.
CPUID Opcode
The CPUID opcode is 0Fh, A2h (as two bytes or A20Fh as a single word). The value in the EAX register, and in some cases the ECX register, specifies what information should be returned. Here are some examples:
- EAX-Register = 0x00 -> CPUID command returns vendor ID in EBX/ECD/EDX registers
- EAX-Register = 0x01 -> CPUID command returns Processor Signature in EAX-register
Vendor ID
The following Processor Signature as well as the Vendor ID are both required for identification of a processor type. The Vendor IDs are for example:[1]
- "AuthenticAMD" (AMD)
- "GenuineIntel" (Intel)
The following Vendor IDs are common in virtual machines with virtualized hardware:
- "KVMKVMKVM" (KVM)
- "Microsoft Hv" (Microsoft Hyper-V)
- "VMwareVMware" (VMware)
- "XenVMMXenVMM" (Xen HVM)
Processor Signature
The processor signature requires the following information:
- Type (0)
- Extended Family, Family
- Extended Model, Model
- Stepping
The information are coded as follows in the EAX register:[2]
| Bit | 31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| EAX descriptions Intel | (reserved) | Extended Family | Ext. Model | (res.) | Type | Family | Model | Stepping | ||||||||||||||||||||||||
| EAX descriptions AMD | (reserved) | ExtFamily | ExtModel | (reserved) | BaseFamily | BaseModel | Stepping | |||||||||||||||||||||||||
| Example of Intel Xeon E3-1220 v6 | 0 | 0 | 0 | 9 | 0 | 6 | e | 9 | ||||||||||||||||||||||||
| Example of AMD EPYC 7251 8-Core | 0 | 0 | 8 | 0 | 0 | f | 1 | 2 | ||||||||||||||||||||||||
To display Family / Model / Stepping for users (e.g., /proc/cpuinfo under Linux), the information is compiled as follows:
| /proc/cpuinfo output
(decimal, not hex) | |||
|---|---|---|---|
| Family | Model | Stepping | |
| rule formulation Intel[2] | IF Family_ID ≠ 0FH
THEN DisplayFamily = Family_ID; ELSE DisplayFamily = Extended_Family_ID + Family_ID; |
IF (Family_ID = 06H or Family_ID = 0FH)
THEN DisplayModel = (Extended_Model_ID « 4) + Model_ID; ELSE DisplayModel = Model_ID; |
|
| Example of Intel Xeon E3-1220 v6 | Ext. Family = 00h
Family = 06h Display Family = 06h = 6 (decimal) Anzeige Family (decimal): 6 |
Ext. Model = 09h
Model = 0eh Display Model = 9eh (hex) = 158 (decimal) Display Model (dezimal): 158 |
9 |
| rule formulation AMD[3] | Family[7:0]=({0000b,BaseFamily[3:0]}+ExtendedFamily[7:0]) | Model[7:0]={ExtendedModel[3:0],BaseModel[3:0]} | |
| example of AMD EPYC 7251 8-Core | ExtFamily = 08h = 8 (decimal)
BaseFamily = 0fh = 15 (decimal) Family = 8 + 15 = 23 (decimal) Display Family (decimal): 23 |
ExtModel = 00h
BaseModel = 01h (hex) Model = 01h (hex) = 1 (decimal) Display Model (decimal): 1 |
2 |
Querying the processor signature
Microcode updates always refer to a certain processor type (processor signature). The processor signature can be read out in the following manner under the respective operating systems:
- Linux:
- Calculation from Family/Model/Stepping (see also Update Intel Microcode under Linux)
- x86info -a
- dmesg | grep -i microcode
[ 0.000000] microcode: microcode updated early to revision 0xfa, date = 2023-07-16
[ 2.188392] microcode: sig=0x806ec, pf=0x80, revision=0xfa
[ 2.188645] microcode: Microcode Update Driver: v2.2.
- Windows: Calculation from Family/Model/Stepping (see also Update of Intel Microcode under Windows)
- VMware: vsish -e cat /hardware/cpu/cpuList/0 (see Update of Intel Microcode under VMware#Reading out current Microcode version)
- FreeBSD: x86info -a (see Check FreeBSD hardware information#x86info)
References
- ↑ CPUID (en.wikipedia.org)
- ↑ 2.0 2.1 Intel 64 and IA-32 Architectures Developer's Manual: Vol. 2A (www.intel.com) Seiten 3-190, 3-204, 3-205 (292, 306, 307 in PDF)
- ↑ Processor Programming Reference (PPR) for AMD Family 17h Model 01h, Revision B1 Processors Chapter 2.1.11.1 CPUID Instruction Function, Page 56
More information
- x86 architecture CPUID (www.sandpile.org)
- https://linux.die.net/man/1/cpuid
- Intel Architecture and Processor Identification With CPUID Model and Family Numbers (software.intel.com, 15.06.2012)
- Developer Guides, Manuals & ISA Documents (developer.amd.com)
- x86 Families and Models List (a4lg.com)
- CPUID - AMD (en.wikichip.org)
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Author: Werner Fischer Werner Fischer, working in the Knowledge Transfer team at Thomas-Krenn, completed his studies of Computer and Media Security at FH Hagenberg in Austria. He is a regular speaker at many conferences like LinuxTag, OSMC, OSDC, LinuxCon, and author for various IT magazines. In his spare time he enjoys playing the piano and training for a good result at the annual Linz marathon relay.
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Translator: Alina Ranzinger Alina has been working at Thomas-Krenn.AG since 2024. After her training as multilingual business assistant, she got her job as assistant of the Product Management and is responsible for the translation of texts and for the organisation of the department.
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