Cache tag directory entry contains modified dirty-bit if the cache is
A
write back
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B
Both (A) and B
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C
write through
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D
Not related with cache write
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Solution
The correct option is A write back option (b)
In write-back cache only modified blocks are written back into main memory; not modified blocks are directly overwritten. It saves memory access time. To keep track of modified blocks one bit is stored in cache tag directory entry for each block: which is known as modified/dirty bit.
In write through cache main memory content is immediate updated a long with cache updation. So no need to keep track of modified block. Hence no any modified/dirty bit needed in cache directory entry.