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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.

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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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