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Performance Assessment

Performance of a CPU is measured in units of 'things per second' (/s or s-1or hertz (Hz)). In other words it tells you how much can be done each second - a sort of work rate.

That means that bigger is better. The more it can do in a second the faster it will complete a task - and hey, we want a fast machine, n'est-ce pas?

For computer, the time for one task is called Response Time or Execution Time

Example questions

Q1. What is the performance of a CPU with a response time of 20 ns?
Q2. What is the performance of a CPU with an execution time of 0.40 ps?

What is meant by the word 'time'?

'Time' when we are dealing with computers means the total time to complete a task.

Time includes:

    • disk accesses,
    • memory accesses,
    • I/O activities,
    • operating system overhead,

There are three ways that this total time is refrerred to, but they all mean the same thing - time from start to finish of a program execution:

  • Real time

    Measured on a clock or watch.

  • Response time

    The response time (in data processing) is the time perceived by the end user is the interval between the instant at which an operator at a terminal enters a request for a response from a computer and the instant at which the first character of the response is received at a terminal.

    In a data system, the system response time is the interval between the receipt of the end of transmission of an inquiry message and the beginning of the transmission of a response message to the station originating the inquiry

  • Elapsed time

    Elapsed time is the time taken from start of computer program to the end. Elapsed real time includes I/O time and all other types of wait. Elapsed Real time is the time measured by an ordinary clock.

An alternative is to just consider the time the processor (CPU) is working only on your program (since multiple processes are running at same time). If we are looking at that definition of time then we call it "CPU execution time" or "CPU time"

How to measure time

How many cycles are required for a program to run? (CPI)

Benchmarks - performance assessment standards.