====== Check x86 CPU feature ======

===== Synopsis =====

    cpuid [--ext] [--ecx] <bit number>

===== Examples =====

=== Check if CPU supports 64-bit operation ("long mode") ===

    cpuid --ext 29 && set arch x86_64 || set arch i386

=== Check if CPU supports physical address extensions ("PAE") ===

    cpuid 6 && set pae yes ||

=== Check if CPU supports hardware virtualisation ===

    cpuid --ecx 5 && set vmx yes ||
    cpuid --ext --ecx 2 && set svm yes ||
    isset ${vmx} || isset ${svm} && set hw_virt yes ||

===== Description =====

Check for the existence of the specified x86 CPU feature using the ''[[http://en.wikipedia.org/wiki/CPUID|CPUID]]'' instruction.  If the ''%%--ext%%'' option is specified then the [[http://support.amd.com/us/Embedded_TechDocs/25481.pdf|extended feature set]] is checked, otherwise the [[http://download.intel.com/design/processor/applnots/24161832.pdf|standard feature set]] is checked.  If the ''%%--ecx%%'' option is specified then the feature set contained in the ''%%%ecx%%'' register is checked, otherwise the feature set contained in the ''%%%edx%%'' register is checked.

Some useful features to check are:

^ Feature set  ^ Register  ^ Bit  ^ Feature  ^ Command  |
| Extended  | ''%%%edx%%''  | 29  ^ Long mode (64-bit)  | ''%%cpuid --ext 29%%''  |
| Standard  | ''%%%edx%%''  | 28  ^ Hyper-threading (HTT)  | ''%%cpuid 28%%''        |
| Standard  | ''%%%edx%%''  | 6   ^ Physical address extensions (PAE)  | ''%%cpuid 6%%''  |
| Standard  | ''%%%ecx%%''  | 5   ^ Intel Virtual Machine Extensions (VMX)  | ''%%cpuid --ecx 5%%''  |
| Extended  | ''%%%ecx%%''  | 2   ^ AMD Secure Virtual Machine (SVM)  | ''%%cpuid --ext --ecx 2%%''  |
| Standard  | ''%%%edx%%''  | 15  ^ Conditional Move (CMOV)  | ''%%cpuid 15%%''  |

===== Command status =====

^ Success   | The specified x86 CPU feature is present       |
^ Failure   | The specified x86 CPU feature is not present   |

===== See also =====

  * ''[[:cmd:set]]''
  * iPXE [[:scripting|scripting]] guide
  * [[:cmd|List of all iPXE commands]]

===== Notes =====

The [[http://download.intel.com/design/processor/applnots/24161832.pdf|standard feature set]] represents the values returned in ''%%%ecx%%'' and ''%%%edx%%'' when ''CPUID'' is called with ''%%%eax=0x00000001%%''.

The [[http://support.amd.com/us/Embedded_TechDocs/25481.pdf|extended feature set]] represents the values returned in ''%%%ecx%%'' and ''%%%edx%%'' when ''CPUID'' is called with ''%%%eax=0x80000001%%''.