Hardware Protocol used to tackle Cache Coherence problems ans. is Directory Protocol only are (a) and (b) is Snoopy Protocol only is MESI protocol only

The question seems to be asking about the hardware protocols used to tackle cache coherence problems. Here are the options:

1. Directory Protocol: This protocol uses a directory to keep track of which caches have a copy of a given block of memory. The directory can be centralized or distributed across multiple nodes. When a cache wants to write to a block, it must first check with the directory.

2. Snoopy Protocol: This protocol is used in bus-based multiprocessor systems. All caches are connected to a common bus and can "snoop" on the bus to see if other caches are requesting or updating a block of memory they have a copy of. If they see such a request, they can update or invalidate their own copy of the block.

3. MESI Protocol: This is a specific type of snoopy protocol. MESI stands for Modified, Exclusive, Shared, and Invalid, which are the four states a block of memory can be in. The protocol ensures that multiple caches can have a shared copy of a block, but only one cache can have an exclusive or modified copy.

So, the answer to the question is that all of the above (Directory Protocol, Snoopy Protocol, and MESI Protocol) are hardware protocols used to tackle cache coherence problems.