Please answer ALL the parts 9 . Suppose you have a word addressable cached memor
ID: 3816688 • Letter: P
Question
Please answer ALL the parts
9. Suppose you have a word addressable cached memory system with the following parameters: tm = 1000ns tc = 100ns
h = 0.90 Block size = 8 words
(a) Calculate the effective memory access time, if upon a cache miss the word is directly read from main memory (i.e., there is a read through policy implemented).
(b) Calculate the effective memory access time with no read through policy. Upon a cache miss, a block is first written to main memory (one word at a time), then the desired block is read from main memory into the cache (one word at a time), and finally the word is read from the cache.
(c) Consider the following options to improve the effective memory access time in part (b):
• (1) Make main memory twice as fast
• (2) Maintain tm = 1000ns, but make the main memory to cache connection 4 words wide
Which of these two options is better, assuming each costs the same? Justify your answer.
Explanation / Answer
a.
Effective memory access time = 100+0.1*1000 = 200ns for each word.
b.
Miss Penalty:
Time to write the block= time to read from cache + time to write to memory = 100*8+1000*8=8800ns.
Time to write to cache = time to read from memory + time to write to cache = 1000*8 + 100*8=8800ns
The time to read the word from cache=100ns
Total time= 8800+8800+100 = 17700ns.
Effective access time = 100 + 0.1*(8800+8800+100) = 1870ns.
c.
(1) Since, the main memory is made twice as fast so the effective access time is calculated as follows: 100+0.1*(4800+4800+100) = 1070ns
(2) Since, the time to read from memory is made as 1000ns so, the effective access time is calculated as follows: 100+0.1*(4400 + 4400 + 100) = 990ns.
Assuming the costs as same, option 2 is better.
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