Why do computers have to do everything at full speed?

Discussion in 'Mac Basics and Help' started by tekno, Nov 4, 2012.

  1. tekno macrumors 6502a

    Oct 15, 2011
    So I'm here doing some work and thought I'd also get a couple of DVDs Handbraking. The noise of my fans going due to the increased heat is really doing my head in!

    Why can't I tell my Mac that this isn't urgent and doesn't need to be done asap? Why does it have to do everything as if I asked for it to be done yesterday?

    I'd rather it used less power, less heat and didn't make such a loud whirring all the time.
  2. WordMasterRice macrumors 6502a

    Aug 3, 2010
    Upstate NY
    If it were to do it slower then the extended time would end up using more power and more heat. There is absolutely no point to artificially slowing it down, you should be able to set it to a lower priority so that if you want to do something it will get a higher priority. Outside of that the fast it does it the more efficiently it is working.
  3. throAU macrumors 68040


    Feb 13, 2012
    Perth, Western Australia
  4. tekno thread starter macrumors 6502a

    Oct 15, 2011
    Do you have any evidence of this? The extra heat and power used for the fans suggests to me energy is being wasted.

    That's a bit like saying driving at 100mph is more economical than driving at 50mph cos it takes half the time to do your journey.
  5. WordMasterRice macrumors 6502a

    Aug 3, 2010
    Upstate NY
    Well I'm a computer engineer so I happen to know something about it. The power used for a fan has about as little to do with overall power consumption as possible. Your CPU uses orders of magnitude more power.

    Your car analogy doesn't hold up because a CPU power curve isn't linear. If your CPU is running at 50% that doesn't mean it's using 50% of the power or generating 50% of the heat.
  6. tekno thread starter macrumors 6502a

    Oct 15, 2011
    So the answer to my "do you have any evidence of this?" is "No".
  7. Weaselboy Moderator


    Staff Member

    Jan 23, 2005
    You could use the Terminal command renice to tell your computer to allocate fewer CPU cycles to Handbrake. I have seen some apps that put a GUI on renice, but have never tried them myself.
  8. pdjudd macrumors 601

    Jun 19, 2007
    Plymouth, MN
    No, he is somewhat right. The fans run no matter what since the system creates heat no matter how much. It isn't a linear system. You can design a system in hardware to generate less heat, but that has nothing to do with what you are talking about.

    You are making a big assumption by saying:
    What is your evidence for this? I can tell you that modern computers generate heat no matter what. That's why the fans operate. They are on right from the get go since. Its based on more factors other than CPU power though. We are talking about mechanical devices here.
  9. snberk103 macrumors 603

    Oct 22, 2007
    An Island in the Salish Sea
    I'm not a computer engineer, but I have done some research on this. So - take this with a grain of salt.

    With nothing else going on, in theory: It takes the same amount of 'work' to 'handbrake' a file whether you do it at full speed or at a tenth of full-speed. The same of 'energy' is used, and therefore the same amount of heat is produced. At full-speed the heat builds up faster than it can naturally radiate away, and yes, your fans may need to kick up a notch. At 1/10 speed the same amount of heat is being produced, it's just being produced over a longer period of time, and some of it (or all of it, perhaps) will have a chance to radiate away before the fans need to kick up a notch.

    It may seem that you use a tiny bit more energy to kick the fans up a notch... but as others have noted, the fans use a negligible bit of electricity. However, there is more. At 1/10 speed the CPU is not completely dormant. Its clock is still ticking, and its always checking to see what it needs to do next. It has a handbraking task in the queue, and it wants to finish it. Every clock cycle it's looping and checking to see if it's time to work on the handbrake job a bit more. Those extra loops and cycles also user up energy. So the extra tiny bit of power you save by not revving up the fans is more than made up for by the extra looping cycles as it waits to go to the next step.


    Why the car analogy doesn't work is because, among other things, you have air friction. The faster you push something through the air, the more turbulence you get ... which creates more drag. If your car was in a vacuum you would see much closer fuel economies... though there are other mechanical drags that increase with speed.

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