[16 marks] Consider a word-addressed computer whose memory latency is 200 cycles

Question

[16 marks] Consider a word-addressed computer whose memory latency is 200 cycles. The hardware bandwidth is 1 word/cycle.The processor manages to sustain 180 outstanding (load) memory references in each and every cycle.

a) [8 marks] Using Little's law, calculate the (potential) software bandwidth in words/cycle arriving at the processor. Does the hardware bandwidth limit you? Show your work.

b) [8 marks] The processor has a cache, with a 1-word cache line, whose hit rate is 95%. Assuming that each arithmetic operation requires one new operand, and that the _peak_ arithmetic performance of the processor is 20 operations/cycle, what is the _sustained_ arithmetic performance of this processor in operations per cycle? Show your work.

Explanation / Answer

1. Using little law

Wait time = 200 cycles

arrvial rate = 1word /cycle

Length of queue using little law = 1 * 200.

Given load is 180. which is well in the limit of Max Queue size of 200.

2. Sustianed athermic performance

95/100 *20 = 19 per cycle sustained bandwidht

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