Suppose we have a multiprocessor system with 256 processors. Each processor has a 2 Megabyte private Write-Back cache with 64-byte cache blocks. The main memory size is 2 Gigabyte.
If we implement a snoopy bus based MESI cache coherence protocol, how many bits of state do we need in the entire system for the coherence protocol implementation?
If we instead implement a directory based cache coherence protocol discussed in the last week, how many bits of state do we need in the entire system for the coherence protocol implementation?
Which of the above two protocols would you choose for this system? Snoopy or Directory? Why?