Mac Pro 2008 8 Core CPU temperatures extremely cool?

Discussion in 'Mac Pro' started by iBug2, Feb 23, 2010.

  1. iBug2 macrumors 68040

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    Jun 12, 2005
    #1
    I have an octo 2.8 which I use at 3.2 overclocked, and I have been running handbrake for 20 hours straight, utilizing all 8 cores. So the machine has been working full capacity for 20 hours, and I check CPU temperatures with Hardware Monitor, and they are 55 degrees. These CPU's are ok up to 100 degrees or so. So how can they stay that cool even at full load?

    I wish I could overclock them even further but RAM's can't be overclocked further so I need to stop at 3.2 Ghz.
     
  2. ZennZero macrumors member

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    Mar 21, 2008
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    London
    #2

    The Mac Pro has pretty great cooling. Have you noticed that your system clock is running fast? That is the main downside to overclocking a MP... But as long as your aren't doing anything that needs accurate timestamps you should be fine.
     
  3. Gonk42 macrumors 6502

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    #3
    That is impressively cool compared to the temperatures reported in the 09 models (over the iTunes bug). I would expect temperatures in the range 70-90 degrees C. What is the Heat Sink temperature? (I don't have a Mac Pro but I believe that the Heat Sink Temp is monitored.) On my Dell workstation the Heat Sinks are around 25 degrees cooler than the junction temp but I think something like 15 degrees is more typical. (It varies with temperature of course.)
     
  4. gotzero macrumors 68040

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    #4
    My 08 runs cool as a cucumber (and quiet) day after day. I would periodically open and dust it out though, even if you are getting good performance. A lot of air moves through that machine, and there are a lot of places to catch dust.

    Your numbers are not out of spec, I am surprised that OCing does not give you a little heat though. Are your fans running between 600-800RPM? That is the baseline for me.
     
  5. iBug2 thread starter macrumors 68040

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    #5
    OC'ing does not effect system clock if you reboot your computer. I just OC and reboot and that's it. As long as you don't shut down your Mac Pro, the OC stays. Even if you boot from another HD/DVD the OC stays. So OC'ing is quite reasonable on 08 Mac Pro's.
     
  6. iBug2 thread starter macrumors 68040

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    #6
    I haven't seen heatsink temperature over 53 degrees on max load.
     
  7. iBug2 thread starter macrumors 68040

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    #7
    Yes all fans are between 600 and 700 even. This machine is the quietest mac I have ever used. My GT8800 used to be extremely noisy but I bought a GTX285, which runs really quiet as well, even on max load.
     
  8. tamvly macrumors 6502a

    tamvly

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    #8
    How do you do the over-clocking?

    I think some mag had a tool, but I am usually distrustful of such utilities.
     
  9. Transporteur macrumors 68030

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    UK
    #9
    You can add 15 - 20° and you've got your core temperature.
    Not that cool any more, isn't it? :p
     
  10. bearcatrp macrumors 68000

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    #10
  11. macz1 macrumors 6502

    macz1

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    Oct 28, 2007
    #11
    Sadly, this tool does not work anymore for me since Snow Leopard...

    Does anybody know if there is apossibility to get it running in 10.6?
     
  12. gotzero macrumors 68040

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    #12
    I would say you are fine if your fans are at that range (which is wonderfully quiet) and your temperatures are fine.

    I run six drives, a full load of RAM, and three graphics cards including a 4870 on a computer that works hard for a good portion of the day, and my temps and fans are fine. It is a fantastically designed system.
     
  13. iBug2 thread starter macrumors 68040

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    #13
    That's the max I have seen though. Usually it's around 37 degrees :)
     
  14. iBug2 thread starter macrumors 68040

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    #14
    No it doesn't work on SL. So I OC my Mac Pro on Leopard and then boot back to SL.

    About the system clock, it speeds it up, but if you reboot your machine it goes away. BUT, not all Mac Pro systems keep their OC after a reboot. 2008 ones do keep it. So just OC and then reboot if you have a 2008 one.
     
  15. Eithanius macrumors 65816

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    Nov 19, 2005
    #15
    I have a 2008 MP 2.8GHz in office on load 24/7, Hardware Monitor register them around lower 50 degrees... ambient 26....
     
  16. doctoree macrumors 6502

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    #16
    I had to lough when I read the thread title :) Normally, people complain about HIGH temperatures and open manny threads for "heat issues".
     
  17. Eithanius macrumors 65816

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    #17
    Well, for once this is one of the very few threads that actually complements the Mac Pro instead of complaints... :p
     
  18. Gonk42 macrumors 6502

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    near Cambridge
    #18
    No magic in the design

    I am a scientist (or at least a computer scientist) and trained as an engineer so I like to get to understand things properly.

    Initially I was very impressed with the low temperatures but on further thought I think it is just an indication that the older Intel architecture of a slow FSB and FBDIMMs mean that the cores themselves are not fully utilised (at least not all eight at once).

    The 09 Mac Pros have at least a good a thermal solution as the 08 model (probably better as they use chips without the heat spreader allowing direct contact with the heatsink and also don't need to allow so much space for the memory as the DDR3 DIMMs don't need the big heat sinks that are found on the FBDIMMs in the 08 model).

    The 09 Mac Pros get hot (see thread on the itunes bug).

    My experience with my Dell workstation (similar to the 09 Mac Pro) shows that the temperature drops with lower utilisation (as you'd expect).

    So I estimate that your Pro is running cooler because it is running at perhaps only 50-60% utilisation of the CPUs, the memory system bottleneck preventing higher utilisation.

    One way to get an estimate is to run the same work load on your system at its standard 2.8GHz clock and then again at the overclocked 3.2GHz. If the cores were at 100% utilization then the speed up would be about 14%. If the cores are only at about 50% - 60% utilization (as indicated by the low 55C temp) then the speed up will only be in the range 7%-9%.

    I am now very curious, so if you have time to do the experiment I'd like to know the result.

    PS
    The experiment will only be accurate if you are running software that is multi-threaded and trying to use all eight cores. For a single threaded application the memory will not be a bottleneck in the same way so the speed up will be proportionally greater.
     
  19. Chilz0r macrumors regular

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    Jul 20, 2007
    #19
    You forgot that the 08 MP is quad-pumped so when you overclock you're increasing the speed of the bus clock i.e. more bandwidth and speed of memory (I think.....LOL!).
     
  20. Gonk42 macrumors 6502

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    #20
    The memory may be faster than it was but the overall bandwidth will still be a lot less than on the Nehalem architecture with its six channels of DDR3 and no front-side bus getting in the way.

    But you're right in that it will complicate things with my suggested experiment. I don't know what it will do to the latency. The latency is large on FBDIMMs and I don't know if simply overclocking them will reduce it.

    The best test would be to run Prime95 but it would probably have to be under Windows rather than OSX. That can be set to just load the cores (by keeping everything small enough for the cache) and then observe the CPU temperatures under 100% load.
     
  21. iBug2 thread starter macrumors 68040

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    Jun 12, 2005
    #21
    The cores are utilized 100% according to activity monitor. I see 750% cpu usage during handbrake ripping. I don't think there's any memory bottleneck when ripping a movie.
     
  22. tamvly macrumors 6502a

    tamvly

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    #22
    Well, now I'm curious why the ZD tool works on Leopard and not on SL.

    Any insights?
     
  23. iBug2 thread starter macrumors 68040

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    Jun 12, 2005
    #23
    No idea, but it shouldn't be too hard to update an application that simple. Why haven't they done it yet I wonder.
     
  24. maghemi macrumors 6502

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    Aug 7, 2009
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    Melbourne Australia
    #24
    Awesome. I've was wondering how you were doing it. I think I'll give this one a try this week. I try and avoid cold starting my machine anyway because I'm using the netkas trick for the GTX 285.

    I'm curious though, does it overclock the memory as well or just the cpu's?

    I ask this because even though the CPU's stay reasonable cool in my 08, the ram gets toasty hot. Even with getting ram with the proper heat spreaders.
     
  25. Gomff macrumors 6502a

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    Sep 17, 2009
    #25
    I'd like to try this on my 2008 machine with the same specs as the OP, except that I'm using a flashed 4870.

    I used to keep an old install of Leopard on one of my partitions but got rid of it when I put the new card in and realised it wasn't supported automatically.

    Does anyone know how I can install Leopard with my 4870 in the machine?
     

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