Suppose you are designing a computer system and are considering a change to your original design. You have run a set of benchmark programs on the original design and obtained some measurements.
The original design had 16 general purpose registers; the enhanced system is to have 32 general purpose registers.
In the original design each ALU instruction had two variants: one with all operands and result being registers and the other variant allowed one source operand to come from memory. In the enhanced system all ALU operands will be in registers; that is, obtaining an operand from memory will no longer be supported. As a result, the compiler will generate a load and the corresponding
register-only ALU operation for every ALU memory reference instruction on the old system.In the benchmark programs, 60% of the ALU instructions must be replaced by a load followed by the register-only ALU operation.Assume that the clock cycle time of the enhanced system is 0.75 times that of the un-enhanced system, and that the CPI of the enhanced system is 0.85 times that of
the un-enhanced system.Suppose the frequency of use of different classes of instructions for the original design are as given in the table below (in terms of percent):
Instruction class Percent
Loads 10%
ALU 70%
Other 20%
a. Estimate how much speedup would be gained from this change. You must.show your work.
b. Would you advise making this change? Why