Hi ,
why do we need Valid bit on block of memory? I know that if Valid bit=0 then it's like data isn't relevant .. if valid=1 then data of the block is relevant .. but how's that help the processor?! if I grab the data from Main memory to cache, then the grabbed data is always available ... and it's relevant .. so it's like valid bit=1 always and just at first transaction the valid bit of the block would be 0.

thanks alot

 

You have a fixed amount of cache memory. If you have new data for the cache, then some old data must discarded. This happens in multiple steps:

1. The block is marked invalid
2. The block is updated with new data
3. The block is marked valid

What is your alternative for doing it?