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Module core.cpuid

Identify the characteristics of the host CPU, providing information about cache sizes and assembly optimisation hints. This module is provided primarily for assembly language programmers.


Some of this information was extremely difficult to track down. Some of the documents below were found only in cached versions stored by search engines! This code relies on information found in:

  • "Intel(R) 64 and IA-32 Architectures Software Developers Manual, Volume 2A: Instruction Set Reference, A-M" (2007).
  • "AMD CPUID Specification", Advanced Micro Devices, Rev 2.28 (2008).
  • "AMD Processor Recognition Application Note For Processors Prior to AMD Family 0Fh Processors", Advanced Micro Devices, Rev 3.13 (2005).
  • "AMD Geode(TM) GX Processors Data Book", Advanced Micro Devices, Publication ID 31505E, (2005).
  • "AMD K6 Processor Code Optimisation", Advanced Micro Devices, Rev D (2000).
  • "Application note 106: Software Customization for the 6x86 Family", Cyrix Corporation, Rev 1.5 (1998)
  • "Geode(TM) GX1 Processor Series Low Power Integrated X86 Solution", National Semiconductor, (2002)
  • "The VIA Isaiah Architecture", G. Glenn Henry, Centaur Technology, Inc (2008).
  • "What every programmer should know about memory", Ulrich Depper, Red Hat, Inc., (2007).
  • "CPU Identification by the Windows Kernel", G. Chappell (2009).
  • "Intel(R) Processor Identification and the CPUID Instruction, Application Note 485" (2009).


Currently only works on x86 and Itanium CPUs. Many processors have bugs in their microcode for the CPUID instruction, so sometimes the cache information may be incorrect.


Name Description
aes Is AES supported
amd3dnow Is AMD 3DNOW supported?
amd3dnowExt Is AMD 3DNOW Ext supported?
amdMmx Are AMD extensions to MMX supported?
avx Is AVX supported
avx2 Is AVX2 supported
cacheLevels The number of cache levels in the CPU.
coresPerCPU Returns number of cores in CPU
dataCaches The data caches. If there are fewer than 5 physical caches levels, the remaining levels are set to size_t.max (== entire memory space)
fma Is FMA supported
fp16c Is FP16C supported
has3dnowPrefetch Is 3DNow prefetch supported?
hasCmov Is cmov supported?
hasCmpxchg16b Is cmpxchg8b supported?
hasCmpxchg8b Is cmpxchg8b supported?
hasFxsr Is fxsave/fxrstor supported?
hasLahfSahf Are LAHF and SAHF supported in 64-bit mode?
hasLzcnt Is LZCNT supported?
hasPclmulqdq Is pclmulqdq supported
hasPopcnt Is POPCNT supported?
hasRdrand Is rdrand supported
hasRdseed Is rdseed supported
hasRdtsc Is rdtsc supported?
hasSha Is SHA supported
hasSysEnterSysExit Is SYSENTER/SYSEXIT supported?
hasVpclmulqdq Is vpclmulqdq supported
hle Is HLE (hardware lock elision) supported
hyperThreading Is hyperthreading supported?
isItanium Is this an IA64 (Itanium) processor?
isX86_64 Is this an Intel64 or AMD 64?
mmx Is MMX supported?
preferAthlon Optimisation hints for assembly code.
preferPentium1 Does this CPU perform better on Pentium I code than Pentium Pro code?
preferPentium4 Does this CPU perform better on Pentium4 code than PentiumPro..Core2 code?
processor Returns processor string, for display purposes only
rtm Is RTM (restricted transactional memory) supported
sse Is SSE supported?
sse2 Is SSE2 supported?
sse3 Is SSE3 supported?
sse41 Is SSE4.1 supported?
sse42 Is SSE4.2 supported?
sse4a Is SSE4a supported?
ssse3 Is SSSE3 supported?
threadsPerCPU Returns number of threads per CPU
vaes Is VEX-Encoded AES supported
vendor Returns vendor string, for display purposes only. Do NOT use this to determine features! Note that some CPUs have programmable vendorIDs.
x87onChip Does it have an x87 FPU on-chip?


Name Description
CacheInfo Cache size and behaviour

Global variables

Name Type Description
datacache CacheInfo[5] Scheduled for deprecation. Please use dataCaches instead.
family uint Warning: This field will be turned into a property in a future release.
model uint Warning: This field will be turned into a property in a future release.
numCacheLevels uint This field has been deprecated. Please use cacheLevels instead.
stepping uint Warning: This field will be turned into a property in a future release.


Don Clugston, Tomas Lindquist Olsen <>


Boost License 1.0