IRIX versions 6.0 and 6.1
IRIX releases 6.0.1 and 6.1 were the first 64-bit releases of IRIX, for the R8000 based POWER Indigo2 and POWER Onyx/Challenge. They were based on IRIX 5.2 and 5.3, respectively, and included Indigo Magic. IRIX 6.0-6.1 were developed before the n32 ABI was standardized, so they only run o32 (IRIX 5.x) and 64-bit n64 binaries.
They are not Y2k compliant, and will not run the common n32 binaries.