Memory and MIMD Computers

• It was easier to invision an MIMD machine than to build one ... the problem is memory

• We are accustomed to a flat, global memory

Memory Coherency

P1

a: 4 5

P2

a:

P3

a: 4

a: 4 5

P1 reads a into cache

P3 reads a into cache

P1 updates a to 5, wt

-- P3 has stale data --

Writeback is worse

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