Editing Distributed shared memory (section)

=== States ===
[[File:Dsm states.png|right|280px|State diagram of a block of memory in a DSM. A block is "owned" if one of the nodes has the block in state EM.]]

A basic DSM will track at least three states among nodes for any given block in the directory.<ref>{{Cite book|title=Fundamentals of Parallel Multicore Architecture|last=Solihin|first=Yan|publisher=Chapman and Hall/CRC|year=2015|isbn=9781482211184|location=Boca Raton, Florida|pages=339–340}}</ref> There will be some state to dictate the block as uncached (U), a state to dictate a block as exclusively owned or modified owned (EM), and a state to dictate a block as shared (S). As blocks come into the directory organization, they will transition from U to EM (ownership state) in the initial node. The state can transition to S when other nodes begin reading the block.

There are two primary methods for allowing the system to track where blocks are cached and in what condition across each node. Home-centric request-response uses the home to service requests and drive states, whereas requester-centric allows each node to drive and manage its own requests through the home.