6. [16 marks] Processor-Memory Bandwidth Consider a computer with a single proce
ID: 3664585 • Letter: 6
Question
6. [16 marks] Processor-Memory Bandwidth Consider a computer with a single processor chip, an interconnection network, and a single memory chip. The _chip bandwidth_ is a hardware limit on how fast you can transfer data on to, or off of, a given chip. The processor chip has a chip bandwidth of 13 GWs/s. The interconnection network has a bisection bandwidth of 14 GWs/s. The memory chip has a chip bandwidth of 7 GWs/s.
a) [8 marks] The hardware limit on processor-memory bandwidth is currently ___ GWs/s. Explain.
b) [8 marks] We add a second memory chip with a chip bandwidth of 7 GWs/s. The bisection bandwidth of the interconnection network is unchanged. The hardware limit on processor-memory bandwidth is now ___ GWs/s. Explain.
Explanation / Answer
Given,
Ans a) Here limit is the throughput of the system which is calculated as shown below:
Processor-memeory bandwidth = min( processor_chip_bandwidth, network_bisection_bandwidth,
memory_chip_bandwidth)
= min(13GWs/s, 14GWs/s, 7GWs/s)
= 7GWs/s
Ans b) When there are two memory chips in effect than they can act in parallel. Hence their bandwidth adds up.
So, Memory chips have effective bandwidth = 7 GWs/s + 7 GWs/s
= 14GWs/s
There fore,
Processor-memeory bandwidth = min( processor_chip_bandwidth, network_bisection_bandwidth,
memory_chip_bandwidth)
= min(13GWs/s, 14GWs/s, 14GWs/s)
= 13GWs/s
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