Choices in Cache Coherence
Machines like the SGI Origin 2000 have a distributed shared memory with a so called directory implementation (pioneered in DASH project at Stanford) of cache coherence
Machines like SGI Cray T3E are distributed memory but do have fast get and put so as to be able to access single variables stored on remote memories
- This gives performance advantage of shared memory without the programming advantage but complex hardware of Origin 2000
Origin 2000 approach does not scale as well as Cray T3E and large Origin 2000 systems must use message passing to link 128 node coherent memory subsystems
Cray T3E offers a uniform (but not as good for small number of nodes) interface
Message passing / distributed memory is natural web model