Image of Modern Operating Systems (3rd Edition)
Image of Beginning Google Maps API 3
Image of RHCE Red Hat Certified Engineer Linux Study Guide (Exam RH302) (Certification Press)
Image of Linux Kernel Development (3rd Edition)

How to Determine Hardware Mode of Intel CPU

Consider the following output:

# grep flags /proc/cpuinfo
flags: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush
       mmx fxsr sse sse2 syscall nx rdtscp lm constant_tsc pni monitor ssse3 lahf_lm

How can you the maximum size of a long that can be used with this CPU? The answer is 64-bit because of the presence of the lm flag.

The following flags can be used to determine the maximum size of a long for a CPU:

  • lm – Long Mode (64 bits)
  • tm – Protected mode (32-bit)
  • rm – Real Mode (16 bits)

If you wish to see the full list of flags returnable by /proc/cpuinfo, look at the header …/arch/x86/include/asm/cpufeature.h in the Linux kernel sources.

Comments are closed.