Lecture Notes for Computer Architecture II - St. Cloud State University

CPU clock speed
1 cycle
1 Hertz =
Second
1
Cycle time =
Clock rate
Page | 120
Several different cases
- One instruction per cycle
- Many instructions per cycle
- Several cycles per instruction
Example:
2GHz machine
If 1 instruction per cycle 2 GIPS
If 2 instructions per cycle 4 GIPS
Performance can be average or peak
GIPS - Peak Performance
GFLOPS - Peak Performance (GFLOPS million floating point operations)
CPU time = Number of instructions * cycle time
To increase performance decrease the CPU time per program
- reduce cycle time
- reduce number of instruction per program
Example:
Machine M1 10 seconds to run Program A
Machine M2 15 seconds to run Program A
How much faster M1 compared to M2?
Solution
Performance M1 CPU time M2 15
= = = 1.5
Performance M2 CPU time M1 10
CPU time = CPU clock cycles per program * clock cycle time
Efforts to decrease CPU clock cycles per program may increase clock cycle time
Performance
- means different things to different people
- two important measures of performance
- throughput