heat production by different CPUs

Discussion in 'MacBook Pro' started by bjj22, Nov 23, 2014.

  1. bjj22 macrumors newbie

    Jun 30, 2013
    This is a question I've been unable to get a satisfactory answer for from my own reading.

    If I have 2 computers, one with a powerful CPU and one with a less powerful CPU, which will produce the more heat when running exactly the same process? Obviously the more more powerful processor has the greater max heat output (TPD, or whatever I should call it), but it's being taxed less than the slower processor (which produces less heat at max but is working closer to that max, relatively speaking).

    I'm sure there will be various factors to consider, so I'll give a real world example:

    I've used Logic for a bit of music production on various different macs, and it's really frustrating when the noisy fans kick in if I'm trying to record something with a microphone. Right now I have a base 2012 macbook air, i.e. not a very powerful computer, and the fans start whining when I'm not doing very much. If I bought a newer, more powerful macbook pro for example, the TPD will probably be higher, but I won't be working it as hard, relative to what it's capable of. So should I expect less fan noise?

    (so in my example, it's more the fan noise I'm interested in, rather than the heat production per se, but still interested to get a definitive answer on the latter)

  2. nerowolfe macrumors member

    Oct 23, 2014
    i7s MBPs use run hot when pushed, and yes they produce more heat but probably have higher TDP as well.

    It's the heat dissipation rate that's really the culprit as to why newer macbooks inevitably run hot quick when taxed and start ramping up the fans. The design of heatsink & aluminum case, they're all good considering laptop dimensions. The same can't be said about their thermal paste and its application.

    If you want real gains in heat dissipation rate, the sure-fire way is to replace the stock thermal paste between cpu and heatsink with one that's superior. Apple may not agree to using anything but their own stock paste though if you ask them to do that, so bear that in mind.
  3. snaky69 macrumors 603

    Mar 14, 2008
    Let's assume a few things here.
    1. The process is not pegging the CPU at 100%
    2. Both CPUs have the same TDP

    Running the same process, the more powerful CPU should technically generate more heat at any given time. BUT, since it is more powerful, it will also accomplish the task faster. All in all, the heat output of both processors should be roughly the same over time.

    Your MBA uses a ULV processor which is a lot less powerful for any given clock speed than a regular mobile processor. So for any given task it is being used a whole lot more(the %Load is higher for any given process than it would be on a MBP). Add to that the fact that the MBA just doesn't have all that much air to move around inside it with the fan, and you'll get what you're experiencing.

    Then again, hearing your fan would mean it is doing its job properly, by not allowing your computer to melt itself into oblivion.

    If you are serious at all about recording, you should not be recording anything in the vicinity of your computer in the first place. You should be using an external audio interface and should be at the very least at the opposite end of the room to your computer so that the mic doesn't pick it up. If you can, I'd move to the next room over for good measure. I'm no audio professional by any stretch of the imagination, but that's what I'd do.
  4. leman macrumors G3

    Oct 14, 2008
    If you give a CPU a task, the CPU will spend all of its resources on this task. There is not really such a thing as 'working less hard relative to what its capable of'. A CPU is either on or off. The 'CPU %' you see in activity monitor simply reflects the CPU time the OS gives to the application. E.g. most UI applications spend most of their time waiting for users input, so they yield their CPU time and are essentially suspended. In comparison, games usually do not yield their CPU time and want to redraw the screen as quickly as possible (this is why games usually utilise close to 100% of the CPU).

    As snaky69 points out, the faster CPU can perform the task quicker and thus produce less heat. However, whether this applies to your case depends on multiple factors, and most of all, on the type of the software you are running in the first place. If its a single short-term computation, the faster computer might be cooler and quieter. If its a type of 'grab-all-CPU-time', like games, then the faster CPU will be just as loud. In the end, the proper solution would to have the application monitor its CPU usage and pause the execution to make sure that its not building up too much heat. Sadly, very few developers bother with such things.

    Going by experience I'd say that if you are running something that makes a MBA turn up its fans, then the same will happen to a quad-core MBP.
  5. bjj22 thread starter macrumors newbie

    Jun 30, 2013

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