i686

i686 is a designation used in the 32-bit x86 (IA-32) ecosystem to denote the target for 686-class processors, beginning with the Intel Pentium Pro and continuing through later generations. It represents a level of instruction set availability and performance optimizations associated with these CPUs, and is commonly used by compilers and operating systems to label builds that expect a Pentium Pro-era feature set or newer.

Historically, i686 sits above the older i386 and i486 targets and below x86-64 in the taxonomy of x86 code generation. In practice, many Linux distributions and software projects publish separate builds for i686 and for older i386 as a way to balance compatibility and performance. An i686 binary is intended for 686-class CPUs and newer, and may not run on very old CPUs that lack certain instructions.

Technical notes about i686 include the presence of improvements introduced with 686-class processors, such as the conditional move (cmov) instruction, which enables certain performance optimizations. The exact instruction set a binary uses depends on compiler options and the CPU’s capabilities. Distributions often provide i686-optimized packages to improve performance on modern 32-bit CPUs while maintaining broad compatibility with all 686-class processors.

In modern contexts, many Linux and BSD systems maintain separate i686 packages alongside broader i386 or 64-bit x86 offerings. While i686 remains relevant for 32-bit systems, some distributions are phasing it out in favor of broader compatibility strategies or 64-bit environments.

See also: i386, i486, i586, x86, x86-64, Pentium Pro.