Basic Write-back Snoopy Cache Design
•Write-back
protocols are more complex than write-through because modified data
remains in the cache
•Introduce
more cache states to handle that
•Modified,
or dirty, the value differs from memory
•Exclusive,
no other cache has this location
•Consider
an MSI protocol with three states:
•Modified
-- data is correct locally, different from memory
•Shared (Valid)
-- data at this location is correct
•Invalid
-- data at this location not correct