ISRO2018-73

Question

For a multi-processor architecture, in which protocol a write transaction is forwarded to only those processors that are known to possess a copy of newly altered cache line?

1. Snoopy bus protocol
2. Cache coherency protocol
3. Directory based protocol
4. None of the above

Comments

Snoopy bus protocol :- https://www.youtube.com/watch?v=19n5Ee82Lco

Directory based protocol :- https://www.youtube.com/watch?v=LSMyKJXkTSo 

I found these helpful :)

Answer 1

Option (C) is correct.

Comments

Are you sure ..? provide any reference link please..:) but ISRO key says option C

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Coherence protocols apply cache coherence in multiprocessor systems. The intention is that two clients must never see different values for the same shared data.

Refer

Answer 2

→ Directory-based coherence uses a special directory to serve instead of the shared bus in the bus based coherence protocols.
→ In directory-based cache coherence, this is done by using this directory to keep track of the status of all cache blocks, the status of each block includes in which cache coherence "state" that block is, and which nodes are sharing that block at that time, which can be used to eliminate the need to broadcast all the signals to all nodes, and only send it to the nodes that are interested in this single block.

So option (c) is right