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apk

Size of each directory entry: ~256 bits = 32 bytes

M[bytes] / 64[bytes/line] = M/64 entries in directory

Size of directory = 0.5*M

dyzz

@apk I wonder if the calculation is slightly off, do we actually need 257 bits per directory entry because of the dirty bit?

CSGuy

@dyzz I don't think a processor needs a presence bit for itself, a processor knows whether or not it has a copy of the data by just looking it up in its cache. So then we can have P-1 presence bits and a dirty bit per directory entry for P bits total. Though the slide itself does imply P presence bits plus a dirty bit.

POTUS

@apk can you explain the reasoning behind M/64? Thanks!

kapalani

@POTUS there is a directory entry for every line in memory. For 64 byte cache line and memory that is M bytes, there will be M/64 directory entries