The OS maps memory across the entire multiprocessor system and attempts to store data near the processors which are using it and to otherwise minimize NUMA effects. For the best scalability, treat the Origin as a distributed memory system. Default compiler optimization level on Origins is only zero. In particular, use the cache effectively.
Memory locality can become a big issue if caching is poor.
The OS can allocate pages of your program's memory anywhere on the Origin, but it attempts to place them near the processor using them. This is great for serial programs and MPI programs, in which every process has it's own private data. As on the Crays, tools are available to help analyze your code. SGI's online manuals tend to be well-written and are often more informative than man pages. Cray Programming Environment 3.5 ARSC will be installing PE3.5 on the T3E and SV1 in the next couple of weeks.