The below table lists the compatibility of CPUs (identified by their available flags) with architectures (as defined by Arch Linux 32). To determine which architecture is suited best for your CPU, check the available flags listed in /proc/cpuinfo.

Architecture CMOV MMX SSE SSE2
i486 CMOV is not required MMX is not required SSE is not required SSE2 is not required
i686 CMOV is required MMX is required SSE is required SSE2 is not required
pentium4 CMOV is required MMX is required SSE is required SSE2 is required

Hint: Currently some i686 packages require SSE2 - which is a bug we're trying to solve. If you experience any problems related to illegal instructions although your cpu should support the architecture (as listed above), please report the issue to us in the forums, on irc or on the bug tracker.