Imagine a computer with no cache, but with a reasonable-size register file. The
ID: 3784244 • Letter: I
Question
Imagine a computer with no cache, but with a reasonable-size register file. The computer has a single floating-point multiplier. The effect of these assumptions is that each floating-point multiply (operation) will, with probability 1, find one of its two operands in the register file, but will need its other operand delivered from memory, and this for _each_ floating-point multiply. Let the floating-point multiplier have a peak performance of 16 GFs/s. At present, the achievable bandwidth from the memory to the processor is 7 GWs/s. (Here, 'W' stands for _word_, not Watt, and, by assumption, one word can hold one floating-point value). K = 10^3 Describe this situation as _compute bound_ or _bandwidth bound_. situation = __________ We buy a second DRAM module and more interconnection links with the same aggregate capacities as the first. Describe this new situation as _compute bound_ or _bandwidth bound_. situation = __________ What would it take to achieve sustained performance equal to the peak performance? answer = _______Explanation / Answer
Answer
a. The given situation is bandwidth bound becuase as there is no cache the other operand needs to be delivered from the memory, so the processing speed will depend on how fast this delivery can be made which in turn is dependant on the bandwidth, hence bandwidth bound.
b.This new situation is compute bound as the shortcoming in the previous shortcoming has been tried to overcome by using a second DRAM module and increased interconnection link which has the same aggregate capacities hence adding up to the previous performance for improvement.
c. By including cache in the system one could achieve sustained performance equal to the peak performance.