I encountered the following section in my operating systems textbook:

At any given point in time, while the program is executing, this process can be uniquely characterized by a number of elements, including the following:

  • Accounting information: May include the amount of processor time and clock time used, time limits, account numbers, and so on.

I am wondering what the difference is between processor time and clock time in this context?

I would greatly appreciate it if the knowledgeable members of this site could please take the time to clarify this.


Processor time refers to the amount of time that the processor itself actually spends working on a task. As a program is executing, the processor is not necessarily being utilized at every second that the program runs – for example, this does not include the time spent waiting for disk or network I/O. Processor time is the sum total amount of time that the CPU was used, as opposed to Clock time (aka "wall-clock time" or "wall time"), which refers literally to regular time as you know it. If a program ran for 10 minutes, that is 10 minutes of clock time.

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