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One of my favorite features in Windows is the built-in Power Plans. I can change how much energy my computer uses - whether I want it to drain power like there's no tomorrow and get incredible performance or whether I want it to run like a turtle and use 1% CPU at the max and barely use any power, or anything in between.

My favorite feature of Power Plans is that I can limit CPU usage. I can make it 30% - or 72% - or 94 percent.

On a Mac, I notice that there are no Power Plans. There is this, but that doesn't do it.

What can I use to limit CPU usage by the entire system (not just one process) on a Mac?

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3 Answers 3

OS X has SpeedStep built in, but as you have noticed you have no/little control over it.

Coolbook is a program that works on pre-Lion versions of OS X but is still not working correctly under Lion? It is also limited to Core Duo and Core 2 Duo processors.

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So is there any way to limit the CPU used by the computer under Lion? –  JavaAndCSharp Mar 28 '12 at 23:07
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yeah, dont open final cut or iMovie. –  XAleXOwnZX Mar 29 '12 at 0:00

Processor usage is processor usage is processor usage. Limiting your CPU to, say, 20% would mean that the same task you want to do anyway would still occur, but take up to 5x longer. The battery life of your machine would actually decrease because it would need to power the display, HDD, etc. for longer to do the same task.

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No, it wouldn't take 5x longer, unless I was using 100% CPU. Example: if I perform a task (starting Chrome, for example), my CPU runs those computations. If Chrome uses 20%, it runs at the same speed. Thus, the same time is taken, which renders your entire point moot. Limiting CPU time can make other background processes that would normally be scanning for viruses/updating/Bitcoin mining slow down. using less CPU and thus less electricity. –  JavaAndCSharp Mar 29 '12 at 0:10
    
you have virus scanning… what? and the computations performed to start chrome wouldn't change in either scenario, your just stretching them out over time –  XAleXOwnZX Mar 29 '12 at 2:17
    
No virus scanning, that was just an example. No, the computations would not be stretched out over time unless they used over 20%, which they do not. Could someone else please back me up on this? –  JavaAndCSharp Mar 29 '12 at 3:15
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okay you lost me, but let me try to better explain what i'm trying to say: opening chrome (for example) would require a certain set of computations. The amount needed WILL NOT change based on any kind of power saving feature. Limiting is access to system resources will cause it to do the same exact computations, but over a longer period of time. It should be noted that there is overhead that runs regardless of how much CPU usage is occurring, such as your LCD backlight, hard drive spinning, etc. –  XAleXOwnZX Mar 30 '12 at 3:39
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@JavaAndCSharp XAleXOwnZX is more right than wrong, even if they're using the wrong terms. SpeedStep decreases CPU voltage (saving power) and clock frequency (slowing down). You do not simply restrict the CPU to 20%, leaving 80% unused - you slow the CPU's clock (and therefore just about everything it does) by a certain amount. This would make all operations take longer. To JavaAndCSharp's point, however, SpeedStep also turns off CPU cores. This won't slow anything down (as they're unused), and might speed up some things as it could increase frequency on other cores and still save power. –  CajunLuke Jun 6 '12 at 18:09

I think that Windows limit it not only by software, but OS X does NOT do that.

They both implements SpeedStep, but OS X offers no fine-grained control, while Windows do.

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