Cache Type => Direct Mapped Cache
Memory Size = 16 Bytes
Cache Size = 8 Bytes
Block Size = 1 Byte
=> Byte Offset = = 0 bits
So, Number of cache blocks = Cache Size / Block Size = 8/1 = 8
=> Index Bits Size = = 3 bits
Cache Index = Memory Block Number % #Cache Blocks = Memory Block Number % 8
Let's understand first memory access 0x48 and how can it map to cache block
Memory Access = 0x48
Memory Access = 0x4C
Memory Access = 0x46
Memory Access = 0x4D
Memory Access = 0x42
Memory Access = 0x4B
Memory Access = 0x45
Memory Access = 0x41
Memory Access = 0x48
Memory Access = 0x4F
Memory Access = 0x4A
Memory Access = 0x47
Memory Access = 0x40
Memory Access = 0x43
Memory Access = 0x4C
Memory Access = 0x4E
Memory Access = 0x40
Memory Access = 0x49
Memory Access = 0x47
Index | Contents | Tag | Contents | Tag |
000 | J | 1001 | 3 | 1000 |
001 | a | 1000 | 7 | 1001 |
010 | 9 | 1000 | ? | 1001 |
011 | V | 1001 | R | 1000 |
100 | s | 1001 | ||
101 | A | 1001 | 8 | 1000 |
110 | p | 1000 | T | 1001 |
111 | 4 | 1001 | d | 1000 |
Total Cache Misses = 15
Total Cache Hits = 4
In Direct Mapped cache, replacement policy is in-built policy as indexed slot is always replaced if it is full. There is no other choice.
The major dis-advatage of this replacement approach is that if multiple block which are mapped to same slot are continuously referenced then they will be swapped in and out multiple times which can lead to thrashing. Also the blocks which are not used for long time but mapped to different cache slot will always be present and never chosen for replacement.
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