Section: Linux Programmer's Manual (4)
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cpuid - x86 CPUID access device
CPUID provides an interface for querying information about the x86 CPU.
This device is accessed by
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
and the upper 32 bits of the file position as the incoming
the latter intended for "counting"
This driver uses
is the minor number,
and on an SMP box will direct the access to CPU
as listed in
This file is protected so that it can be read only by the user
or members of the group
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
is reported by the kernel in cooked form either in
or through subdirectories in
Direct CPUID access through this device should only
be used in exceptional cases.
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
Very old x86 CPUs don't support CPUID.
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.
This page is part of release 3.74 of the Linux
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
- SEE ALSO