IP26&28 Indigo2s, all Onyxes, Origins and big Challenges are also full 64-bit. But, that doesn't really mean much practically speaking- almost everything is compiled in n32 "hybrid" mode, which will run on any R4k or better with IRIX 6.2+. In fact, n32 is what SGI recommends becasue it's faster in processing and, I believe, slightly more memory efficient.