Valid Bits
Byte
Byte
tag of A
Memory
Proc.
Tag
Data Block
V
tag of B
<A>
<A+1>
<B>
<B+1>
0
1
0
1
0
Valid bit must be 1 for cache line to HIT.
At power-up or reset, we set all valid bits to 0.
Set valid bit to 1 when cache line is first replaced.
Flush cache by setting all valid bits to 0, under external program control.
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