In the computer architecture, the performance of the CPU is important because it affects on the total process performance.
We have to consider about many things. For example, some CPU's performance is better than other CPU. However, if the price of this CPU much higher than others, we cannot easily choose it. So, we have to think about cost and performance.
However, in this post, I will try to explain about the Time rather than Cost.
Time
There are two terms in the time.
- Response Time (Latency)
-> How long does it take for my job? - Throughput
-> How many jobs can the machine run at once?
These are important elements about the view of the time.
Performance
If we have some informations about the CPU time, then we can calculate the performance. By using this performance, we can compare to CPU.
Suppose that some CPU's execution time is 0.1. We can use this execution time to extract performance of this CPU. Finally, we can get the performance 10.
In addition, we want to compare CPUs. So, if we divide Performance by Performance, we can get the ratio about the performance.
Also, there are another concept related with performance.
We have to use clock cycle to pass our information to other registers, control units, etc.
To use this clock, we should know about Clock period and Clock frequency.
CPU Time
We can get CPU time with this expression.
- CPU time = CPU Clock Cycles * Clock Cycle Time
In other words, we can use Clock Rate.
So, finally we can express CPU Time = CPU Clock Cycles / Clock Rate.
Finally, we have to know about the expression.
CPU Time = Instruction / Program X Clock Cycles / Instruction X Second / Clock Cycle
