A dog by what metric? In 1994 IRIX was the first 64 bit Unix kernel running on the first 64 bit workstation. In 1997, the same IRIX 6.5 could run on machines from 100Mhz/16MB to 512 cpus monsters. IRIX had really a nice, easy user interface, and many features (real-time IOs, /hw virtual filesystems giving a hint of /proc and /sys long before they came into existence, modular kernel, full 32 bits compatibility on 64 bits machines...) that were long to come on other OS.