libcpuid is a small C library for x86 CPU detection and feature extraction.
Using it, you can:

  - Get the processor vendor, model, brand string, code name, etc.
  - Get information about CPU features such as: number of cores or logical
    CPUs, cache sizes, CPU clock, etc.
  - Check if the processor implements a specific instruction set such as
    SSE2 or 3DNow!
  - Execute the CPUID and RDTSC instructions in a portable way
  - And have this all in your commercial application, without getting into
    trouble, due to permissive license

Reference utility (rather advanced and useful on its own) is also provided.

WWW: http://libcpuid.sourceforge.net/