I'm reading about Unix in a book "The design of UNIX operating system".

But, in the text middle of process state (e.g wakeup, interrupt), there is term 'raise processor execution level'.

What does "raise processor execution level" mean?

  • 1
    If you "can't understand" something there is no need to ask, because you would not understand any answer you would get ;-)
    – Anthon
    Feb 13, 2016 at 15:09
  • 1
    This could mean different things depending on the context. Please give sufficient context (at least the whole sentence, possibly more, whatever is necessary to understand what the author is saying). Feb 13, 2016 at 21:49

2 Answers 2


"Raise processor execution level" means to temporarily block all interrupts so that the kernel can get some critical (by definition, non-interruptible) task completed.

Reference: Operating Systems by I. A. Dhotre

I hope you enjoy reading The Design of the UNIX Operating System. I haven't read that one since back when books were printed on thin slices of processed dead trees. (Sadly, it appears that this remains the only form in which this otherwise excellent book is offered. How quaint!) Do keep in mind that the theoretical design, while valuable to understand, isn't always exactly what gets implemented.

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    processed dead trees, eh? :-) i like that.
    – gerhard d.
    Feb 13, 2016 at 19:08

On a modern OS you can have hounded of programs (services or processes if you wish) running at the same time on a limited number of CPU cores, so there must be a way to define which one has the highest priority over the other ones, that measure is the processor execution level, they range from -20 (highest priority) to 19 (lowest priority)

you can make a program and increase or lower its execution level, this will be translated into getting more or low attention from the kernel and effectively making it run faster or slower



  • 1
    do not mistake user priority (e.g. nice-ness) with processor being turn from user mode to privilege mode, which sound more like what OP is asking.
    – Archemar
    Feb 13, 2016 at 16:52

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