考虑一个具有4组和总共8个高速缓存块(0-7)的2路组关联高速缓存存储器，以及具有128个块(0-127)的主存储器。如果使用LRU策略替换高速缓存块，则在以下顺序的存储块引用之后，高速缓存中将存在哪些存储块。假设最初缓存中没有当前作业中的任何内存块?
0 5 3 9 7 0 16 55
(A) 0 3 5 7 16 55
(B) 0 3 5 7 9 16 55
(C) 0 5 7 9 16 55
(D) 3 5 7 9 16 55答案： (C)
解释：
2-way set associative cache memory, .i.e K = 2.
No of sets is given as 4, i.e. S = 4 ( numbered 0 - 3 )
No of blocks in cache memory is given as 8, i.e. N =8 ( numbered from 0 -7)
Each set in cache memory contains 2 blocks.
The number of blocks in the main memory is 128, i.e M = 128. ( numbered from 0 -127)
A referred block numbered X of the main memory is placed in the
set numbered ( X mod S ) of the the cache memory. In that set, the
block can be placed at any location, but if the set has already become
full, then the current referred block of the main memory should replace
a block in that set according to some replacement policy. Here
the replacement policy is LRU ( i.e. Least Recently Used block should
be replaced with currently referred block).
X ( Referred block no ) and
the corresponding Set values are as follows:
X-->set no ( X mod 4 )
0--->0 ( block 0 is placed in set 0, set 0 has 2 empty block locations,
block 0 is placed in any one of them )
5--->1 ( block 5 is placed in set 1, set 1 has 2 empty block locations,
block 5 is placed in any one of them )
3--->3 ( block 3 is placed in set 3, set 3 has 2 empty block locations,
block 3 is placed in any one of them )
9--->1 ( block 9 is placed in set 1, set 1 has currently 1 empty block location,
block 9 is placed in that, now set 1 is full, and block 5 is the
least recently used block )
7--->3 ( block 7 is placed in set 3, set 3 has 1 empty block location,
block 7 is placed in that, set 3 is full now,
and block 3 is the least recently used block)
0--->block 0 is referred again, and it is present in the cache memory in set 0,
so no need to put again this block into the cache memory.
16--->0 ( block 16 is placed in set 0, set 0 has 1 empty block location,
block 0 is placed in that, set 0 is full now, and block 0 is the LRU one)
55--->3 ( block 55 should be placed in set 3, but set 3 is full with block 3 and 7,
hence need to replace one block with block 55, as block 3 is the least
recently used block in the set 3, it is replaced with block 55.
因此，存在于高速缓冲存储器中的主要存储块是： 0、5、7、9、16、55。
(注意：块3不存在于高速缓存中，已被块55代替)
阅读以下文章，以了解与上述问题相关的更多信息：
高速缓存存储器
缓存组织|介绍这个问题的测验