NAME

       cpuid - x86 CPUID access device

DESCRIPTION

       CPUID provides an interface for querying information about the x86 CPU.

       This device is accessed by lseek(2) or pread(2) to the appropriate CPUID level and reading
       in chunks of 16 bytes.  A larger read size means multiple reads of consecutive levels.

       The lower 32 bits of the file position is used as the incoming %eax, and the upper 32 bits
       of  the  file position as the incoming %ecx, the latter intended for "counting" eax levels
       like eax=4.

       This driver uses /dev/cpu/CPUNUM/cpuid, where CPUNUM is the minor number, and  on  an  SMP
       box will direct the access to CPU CPUNUM as listed in /proc/cpuinfo.

       This  file  is  protected  so that it can be read only by the user root, or members of the
       group root.

NOTES

       The CPUID instruction can be directly  executed  by  a  program  using  inline  assembler.
       However  this  device  allows  convenient  access  to  all  CPUs  without changing process
       affinity.

       Most of the information in cpuid is reported by  the  kernel  in  cooked  form  either  in
       /proc/cpuinfo  or  through subdirectories in /sys/devices/system/cpu.  Direct CPUID access
       through this device should only be used in exceptional cases.

       The cpuid driver is not auto-loaded.  On  modular  kernels  you  might  need  to  use  the
       following command to load it explicitly before use:

            $ modprobe cpuid

       There is no support for CPUID functions that require additional input registers.

       Very old x86 CPUs don't support CPUID.

SEE ALSO

       Intel Corporation, Intel 64 and IA-32 Architectures Software Developer's Manual Volume 2A:
       Instruction Set Reference, A-M, 3-180 CPUID reference.

       Intel Corporation, Intel Processor Identification and the CPUID  Instruction,  Application
       note 485.

COLOPHON

       This  page  is  part of release 4.04 of the Linux man-pages project.  A description of the
       project, information about reporting bugs, and the latest version of  this  page,  can  be
       found at http://www.kernel.org/doc/man-pages/.