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What is the tag in cache?
A tag is said to be a matching tag if, after decoding a CPU address from a pending read or write, the tag field of the CPU address matches the tag associated with a cache block at the cache address given by (index, offset). Note that an optimized cache will take shortcuts, as compared to the state transitions below.
How do you find a block in a cache?
To search a word in the cache
- The set is identified by the index bits of the address.
- The tag bits derived from the memory block address are compared with the tag bits associated with the set. If the tag matches, then there is a cache hit and the cache block is returned to the processor.
Is cache address is used for a tag?
For a 4-way associative cache each set contains 4 cache lines. Each cache line consists of a “tag” and a “data” field. There is also a “valid” bit, which is not shown. The tag portion of the request address is compared to all of the tag fields in the selected set….
| 18 | 10 | 4 |
|---|---|---|
| TAG | SET | OFFSET |
What is block number in cache?
cache block – The basic unit for cache storage. May contain multiple bytes/words of data. cache line – Same as cache block. The number of blocks per set is deter- mined by the layout of the cache (e.g. direct mapped, set-associative, or fully associative). tag – A unique identifier for a group of data.
How to calculate the number of tag in a cache?
The index for a direct mapped cache is the number of blocks in the cache (12 bits in this case, because 2 12=4096.) Then the tag is all the bits that are left, as you have indicated.
How do you find the cache address of a block?
Use the set index to determine which cache set the address shouldreside in. For each block in the corresponding cache set, compare thetag asso-ciated with that block to the tag from the memory address. If there isa match, proceed to the next step. Otherwise, the data is not in thecache.
A word is 4 bytes (or 32 bits) so the question just need to be “…in which each block has 8 words” The answer is – Each block is 32 bytes (8 words), so we need 5 offset bits to determine which byte in each block – Direct-mapped => number of sets = number of blocks = 4096 => we need 12 index bits to determine which set
How to calculate the number of bits in the cache field?
Calculate the number of bits in the TAG, SET, and OFFSET fields of a main memory address. Answer Since there are 16 bytes in a cache block, the OFFSET field must contain 4 bits (24= 16). To determine the number of bits in the SET field, we need to determine the number of sets.