CPUID(4)						     Linux Programmer's Manual							  CPUID(4)

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 only be read 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 ref-
       erence.

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

COLOPHON

       This  page is part of release 3.44 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2009-03-31								  CPUID(4)