virtually/physically tagged caches

Question

can some one please clearly explain ,what is

1.    virtually indexed virtually tagged cache

2.    physically indexed physically tagged cache

3.    virtually indexed physicaly tagged cache

it is very confusing ,these concepts are used in finding effective memory access in questions of gate.

Comments

<<#arjun sir >>

Answer 1

These things have been confusing me also from a long time.

Well I can tell u what i know about virtually indexed physically tagged cache VIPT. Virtual address is divided into Virtual page no and offset. Now we will determine the set index bits from this offset part and will start parallel search in the cache because we know the set/line no. And simultaneously the VPN is sent to TLB for translation into the physical page no PPN. Now we have the physical address as well as the tag bits ready. And we can compare them for hit or miss. Thats the idea of VIPT cache.

Comments

so you mean in VIPT cache,cache and TLB are worked upon simultaneously and not sequentially??

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yeah they are worked on parallel and that for sure. Thats the advantage we get.

I dont understand the homonym problem in virtual caches? i wish arjun sir explains this in detail.

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https://www.youtube.com/watch?v=YbE91A7dNAs 

this might help.

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In VIPT,

What i know is---> Cache has some frames(whole frame) of MM which contains all tag bits of frame/page mapped in its frame. Then what are we checking in Cache with those tag bits?

Edit: Got it