Hi, i need help for the following question: computer A has a clock cycle time of 250ps and a CPI of 2.0 for some program, and computer B has a clock time of 500ps and a CPI of 1.2 for the same program. Which computer is faster for this program and by how much ? Also, i will post the second question later.

Computer A is faster.
Proof:
Each computer is executing the same program (with the same inputs), so the number of instructions is the same; call this number N
First, find the number of clock cycles for each computer
CPU Clock cyclesA = N instructions x 2.0 cycles/instruction
CPU Clock cyclesB = N instructions x 1.2 cycles/instruction
Next, compute the CPU time for each computer
CPU timeA = CPU Clock cyclesA x Clock cycle timeA
= N x 2.0 x 250 ps = 500 x N ps
CPU timeB = CPU Clock cyclesB x Clock cycle timeB
= N x 1.2 x 500 ps = 600 x N ps
Computer A takes less time and is thus faster.

Dermie: Computer A is faster.
Proof:
Each computer is executing the same program (with the same inputs), so the number of instructions is the same; call this number N
First, find the number of clock cycles for each computer
CPU Clock cyclesA = N instructions x 2.0 cycles/instruction
CPU Clock cyclesB = N instructions x 1.2 cycles/instruction
Next, compute the CPU time for each computer
CPU timeA = CPU Clock cyclesA x Clock cycle timeA
= N x 2.0 x 250 ps = 500 x N ps
CPU timeB = CPU Clock cyclesB x Clock cycle timeB
= N x 1.2 x 500 ps = 600 x N ps
Computer A takes less time and is thus faster.

thanks.

this is the 2nd question, A program run in 10s on computer A, which has a 4GHZ clock. A computer designer wants to build a computer B, that will run this program in 6s.the designer has determined that a substantial increase in the block rate is possible, but this increase will affect the rest of the CPU design, causing computer B to require 1.2 times as many clock cycles as computer A for this program. What clock rate should the designer target ?