How can I identify if my CPU is using 32-bit or 64-bit instruction set? On a Linux systems this question can be easily answered by running a command:

cat /proc/cpuinfo

what we are interest in here is a flags row which indicates a CPU's capabilities / features. These CPU capabilities are defined with a kernel's header file /usr/src/linux-headers/include/asm-x86/cpufeature.h For instance flag lm is defined in cpufeature.h header file as :

#define X86_FEATURE_LM          (1*32+29) /* Long Mode (x86-64) */

which means that if your CPU has lm flag listed by cat /proc/cpuinfo command it is using 64-bit instruction set. Here is a simple bash script to identify if your CPU is using 32-bit or 64-bit instruction set. This script is based on the information retrieved from cat /proc/cpuinfo command:

#!/bin/bash

if grep -q lm /proc/cpuinfo ; then
echo "Your CPU has 64-bit instruction set"
else
echo "Your CPU hase 32-bit or 16-bit instruction set"
fi

In fact there is more what we can learn about our CPU when matching cat /proc/cpuinfo with kernel's header file cpufeature.h. Here are flags of my CPU:

flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe
nx lm constant_tsc arch_perfmon pebs bts pni monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr lahf_lm

and here is a top part of macro definition of cpufeature.h:

/* Intel-defined CPU features, CPUID level 0x00000001 (edx), word 0 */
#define X86_FEATURE_FPU (0*32+ 0) /* Onboard FPU */
#define X86_FEATURE_VME (0*32+ 1) /* Virtual Mode Extensions */
#define X86_FEATURE_DE (0*32+ 2) /* Debugging Extensions */
#define X86_FEATURE_PSE (0*32+ 3) /* Page Size Extensions */
#define X86_FEATURE_TSC (0*32+ 4) /* Time Stamp Counter */
#define X86_FEATURE_MSR (0*32+ 5) /* Model-Specific Registers, RDMSR, WRMSR */
#define X86_FEATURE_PAE (0*32+ 6) /* Physical Address Extensions */
#define X86_FEATURE_MCE (0*32+ 7) /* Machine Check Architecture */
#define X86_FEATURE_CX8 (0*32+ 8) /* CMPXCHG8 instruction */
#define X86_FEATURE_APIC (0*32+ 9) /* Onboard APIC */
#define X86_FEATURE_SEP (0*32+11) /* SYSENTER/SYSEXIT */
#define X86_FEATURE_MTRR (0*32+12) /* Memory Type Range Registers */
#define X86_FEATURE_PGE (0*32+13) /* Page Global Enable */
#define X86_FEATURE_MCA (0*32+14) /* Machine Check Architecture */
#define X86_FEATURE_CMOV (0*32+15) /* CMOV instruction (FCMOVCC and FCOMI too if FPU present) */
#define X86_FEATURE_PAT (0*32+16) /* Page Attribute Table */
#define X86_FEATURE_PSE36 (0*32+17) /* 36-bit PSEs */
#define X86_FEATURE_PN (0*32+18) /* Processor serial number */
#define X86_FEATURE_CLFLSH (0*32+19) /* Supports the CLFLUSH instruction */
#define X86_FEATURE_DS (0*32+21) /* Debug Store */
#define X86_FEATURE_ACPI (0*32+22) /* ACPI via MSR */
#define X86_FEATURE_MMX (0*32+23) /* Multimedia Extensions */
#define X86_FEATURE_FXSR (0*32+24) /* FXSAVE and FXRSTOR instructions (fast save and restore */
/* of FPU context), and CR4.OSFXSR available */
#define X86_FEATURE_XMM (0*32+25) /* Streaming SIMD Extensions */
#define X86_FEATURE_XMM2 (0*32+26) /* Streaming SIMD Extensions-2 */
#define X86_FEATURE_SELFSNOOP (0*32+27) /* CPU self snoop */
#define X86_FEATURE_HT (0*32+28) /* Hyper-Threading */
#define X86_FEATURE_ACC (0*32+29) /* Automatic clock control */
#define X86_FEATURE_IA64 (0*32+30) /* IA-64 processor */

/* AMD-defined CPU features, CPUID level 0x80000001, word 1 */
/* Don't duplicate feature flags which are redundant with Intel! */
#define X86_FEATURE_SYSCALL (1*32+11) /* SYSCALL/SYSRET */
#define X86_FEATURE_MP (1*32+19) /* MP Capable. */
#define X86_FEATURE_NX (1*32+20) /* Execute Disable */
#define X86_FEATURE_MMXEXT (1*32+22) /* AMD MMX extensions */
#define X86_FEATURE_GBPAGES (1*32+26) /* GB pages */
#define X86_FEATURE_RDTSCP (1*32+27) /* RDTSCP */
#define X86_FEATURE_LM (1*32+29) /* Long Mode (x86-64) */
#define X86_FEATURE_3DNOWEXT (1*32+30) /* AMD 3DNow! extensions */
#define X86_FEATURE_3DNOW (1*32+31) /* 3DNow! */

/* Transmeta-defined CPU features, CPUID level 0x80860001, word 2 */
#define X86_FEATURE_RECOVERY (2*32+ 0) /* CPU in recovery mode */
#define X86_FEATURE_LONGRUN (2*32+ 1) /* Longrun power control */
#define X86_FEATURE_LRTI (2*32+ 3) /* LongRun table interface */

/* Other features, Linux-defined mapping, word 3 */
/* This range is used for feature bits which conflict or are synthesized */
#define X86_FEATURE_CXMMX (3*32+ 0) /* Cyrix MMX extensions */
#define X86_FEATURE_K6_MTRR (3*32+ 1) /* AMD K6 nonstandard MTRRs */
#define X86_FEATURE_CYRIX_ARR (3*32+ 2) /* Cyrix ARRs (= MTRRs) */
#define X86_FEATURE_CENTAUR_MCR (3*32+ 3) /* Centaur MCRs (= MTRRs) */
/* cpu types for specific tunings: */
#define X86_FEATURE_K8 (3*32+ 4) /* Opteron, Athlon64 */
#define X86_FEATURE_K7 (3*32+ 5) /* Athlon */
#define X86_FEATURE_P3 (3*32+ 6) /* P3 */
#define X86_FEATURE_P4 (3*32+ 7) /* P4 */
#define X86_FEATURE_CONSTANT_TSC (3*32+ 8) /* TSC ticks at a constant rate */
#define X86_FEATURE_UP (3*32+ 9) /* smp kernel running on up */
#define X86_FEATURE_FXSAVE_LEAK (3*32+10) /* FXSAVE leaks FOP/FIP/FOP */
#define X86_FEATURE_ARCH_PERFMON (3*32+11) /* Intel Architectural PerfMon */
#define X86_FEATURE_PEBS (3*32+12) /* Precise-Event Based Sampling */
#define X86_FEATURE_BTS (3*32+13) /* Branch Trace Store */
/* 14 free */
/* 15 free */
#define X86_FEATURE_REP_GOOD (3*32+16) /* rep microcode works well on this CPU */
#define X86_FEATURE_MFENCE_RDTSC (3*32+17) /* Mfence synchronizes RDTSC */
#define X86_FEATURE_LFENCE_RDTSC (3*32+18) /* Lfence synchronizes RDTSC */

/* Intel-defined CPU features, CPUID level 0x00000001 (ecx), word 4 */
#define X86_FEATURE_XMM3 (4*32+ 0) /* Streaming SIMD Extensions-3 */
#define X86_FEATURE_MWAIT (4*32+ 3) /* Monitor/Mwait support */
#define X86_FEATURE_DSCPL (4*32+ 4) /* CPL Qualified Debug Store */
#define X86_FEATURE_EST (4*32+ 7) /* Enhanced SpeedStep */
#define X86_FEATURE_TM2 (4*32+ 8) /* Thermal Monitor 2 */
#define X86_FEATURE_CID (4*32+10) /* Context ID */
#define X86_FEATURE_CX16 (4*32+13) /* CMPXCHG16B */
#define X86_FEATURE_XTPR (4*32+14) /* Send Task Priority Messages */
#define X86_FEATURE_DCA (4*32+18) /* Direct Cache Access */

/* VIA/Cyrix/Centaur-defined CPU features, CPUID level 0xC0000001, word 5 */
#define X86_FEATURE_XSTORE (5*32+ 2) /* on-CPU RNG present (xstore insn) */
#define X86_FEATURE_XSTORE_EN (5*32+ 3) /* on-CPU RNG enabled */
#define X86_FEATURE_XCRYPT (5*32+ 6) /* on-CPU crypto (xcrypt insn) */
#define X86_FEATURE_XCRYPT_EN (5*32+ 7) /* on-CPU crypto enabled */
#define X86_FEATURE_ACE2 (5*32+ 8) /* Advanced Cryptography Engine v2 */
#define X86_FEATURE_ACE2_EN (5*32+ 9) /* ACE v2 enabled */
#define X86_FEATURE_PHE (5*32+ 10) /* PadLock Hash Engine */
#define X86_FEATURE_PHE_EN (5*32+ 11) /* PHE enabled */
#define X86_FEATURE_PMM (5*32+ 12) /* PadLock Montgomery Multiplier */
#define X86_FEATURE_PMM_EN (5*32+ 13) /* PMM enabled */

/* More extended AMD flags: CPUID level 0x80000001, ecx, word 6 */
#define X86_FEATURE_LAHF_LM (6*32+ 0) /* LAHF/SAHF in long mode */
#define X86_FEATURE_CMP_LEGACY (6*32+ 1) /* If yes HyperThreading not valid */

Here are some features of my CPU as retrieved from /proc/cpuinfo:

  • vme - Virtual Mode Extensions
  • mmx - Multimedia Extensions
  • mce - Machine Check Architecture


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