IA-32

Intel IA-32 refers to the instruction set for 32-bit Intel CPUs, first implemented in the 80386 CPU, and by far the most widespread CPU architecture. The IA-32 instruction set is the basis of the Intel Pentium and Xeon ranges, AMD's Athlon and Opteron CPUs, and every other "Intel-compatible" CPU.

All modern CPUs implement extensions on top of the basic 386 instruction set, such as SSE and SIMD. Support for these extensions varies by CPU.

64-bit extensions
Intel originally intended to enter the 64-bit CPU market with the Itanium CPU, implementing the IA-64 instruction set and not compatible with IA-32 CPUs (although it provided an IA-32 emulation layer). However, after AMD extended IA-32 with 64-bit capabilities in their Opteron CPU, Intel responded with the Opteron-compatible EM64T extensions, which are supported by most recent Intel CPUs.