CSC 252 Lecture Notes - Lecture 3: Register File
21 Feb 2017
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Response time: how long it takes to do a task. In this example, latency = 2. 5ns (assume 2ghz) Throughput = 1 / 2. 5ns = 2 giga-instructions/s. The processor wants to read a 64b data block from memory. Bus speed = 1ghz (cycle = 1ns) Response time: measured from point request is made until point request is complete = 108ns. Because it runs at 1ghz, i can run 1g instructions in a second. Latency = 101ns (100ns for unloaded latency [wait period before you can go] + During the data transfer, the main memory has nothing to do, so it can access data instead of waiting (i. e. transfer time and unloaded latency times overlap) Basically, we can do main memory accesses back to back. Therefore response time = 908ns e. g. does doubling the bus width help more or less than reducing main memory latency. This would depend on your expected transfer size and frequency.
