Memory Architecture: Shared Memory

SHARED MEMORY (Without Threads)
CHARACTERISTICS	·        Multiple processes operate independently while sharing the same resources (memory)      ·        Changes in a mem location effected by one      processor are visible to all other processors      ·        Two types: UMA and NUMA

UMA	NUMA
1.    Commonly represented by SMPs  (symmetric multiple processors)          2.    Processors are identical          3.    Same access and access time to mem     4.    Aka CC-UMA (cache-coherent UMA)	Made by physically linking 2 or more SMP machines                  Not all processors have same access time to mem                      Known as CC-UMA only if cache-coherency is maintained                Memory across link is slower

CACHE COHERENCY:

• if one processor updates a location in SHARED MEMORY, all the other processors know about the update
• accomplished at hardware level

by LUA XIN LIN B031210345