Overclock GPU under OS X

Discussion in 'iMac' started by Neryus, Apr 20, 2015.

  1. Neryus macrumors member

    Joined:
    Jun 25, 2013
    #1
    Hi guys!

    I have an iMac late 2013 with the NVIDIA 780M graphics card. As I read on multiple sources, Apple likes to underclock their GPUs in OS X, to avoid the fan beeing noisy.

    Is there a possibility to change the clock of the GPU to normal under OS X? There used to be tools like Zeus that were able to do this several years ago, but I couldn't find anything working with newer Macs and Yosemite.

    Are there tools to do this?
     
  2. The-Pro macrumors 65816

    Joined:
    Dec 2, 2010
    Location:
    Germany
    #2
    well if you have windows installed you can check what the clock speeds are actually at. Install GPUz, it will tell you the current clocks and max clocks
    I have not heard of apple underclocking the 780 in the iMac. If they did there would be a rage thread here somewhere :D
    I do not think a solution for overclocking in OSX exists at the moment :(
     
  3. jblagden macrumors 65816

    jblagden

    Joined:
    Aug 16, 2013
    #3
    Windows Overclock

    If a graphics card is overclocked in Windows, will the overclocking work in OS X or will there be no change in performance in OS X?
     
  4. The-Pro macrumors 65816

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    #4
    overclocking in windows will only overclock it in windows. No difference in OSX.
     
  5. jblagden macrumors 65816

    jblagden

    Joined:
    Aug 16, 2013
    #5
    Okay

    Oh. I was hoping that the changes would be implemented in the BIOS of the graphics card. I guess I'd have to use something like NiBiTor for that.
     
  6. h9826790 macrumors G4

    h9826790

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    Hong Kong
    #6
    To OC a GPU under the current OSX is not recommended. It require to flash the graphic card. That means for a computer like iMac, the process may kill the whole computer, and no easy fix.
     
  7. jblagden macrumors 65816

    jblagden

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    Aug 16, 2013
    #7
    Okay. By the way, the graphics card I might overclock is a desktop card, the GT 740.
     

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  8. h9826790 macrumors G4

    h9826790

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    #8
    OK then. I am not an expert for that card. However, it's possible if the card is flash-able.

    1) Go to Windows
    2) Use GPUZ to dump the BIOS
    3) Back up that ROM x2
    4) Hex edit it or use any tool that good for that particular ROM image
    5) Flash it back to the card

    Then the card is OCed in OSX. Of course, it takes lots of time to get the clock / voltage right (if you want to max it out safely).
     
  9. jblagden macrumors 65816

    jblagden

    Joined:
    Aug 16, 2013
    #9
    Thanks

    Okay, thanks. I think I would just use NiBiTor in OS X.

    I have one more question: Would 52 megahertz count as a minor increase in clock speed?
     
  10. The-Pro macrumors 65816

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    #10
    Highly unlickely you will see any sort of significant improvement from a 52MHz higher clock speed.
     
  11. jblagden macrumors 65816

    jblagden

    Joined:
    Aug 16, 2013
    #11

    Okay, thanks. I thought it would only be a minor improvement. I just thought it best to ask since I don't have any hands-on experience with graphics cards.
     
  12. VicLev macrumors member

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    Jun 6, 2013
    #12
    have you managed to actually dump the vbios from 780m?
     
  13. jblagden macrumors 65816

    jblagden

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    Aug 16, 2013
    #13
    780m? I think you've got the wrong guy. I don't have any laptop GPUs, let alone a 780m.
     
  14. caincha macrumors newbie

    caincha

    Joined:
    Jul 15, 2012
    #14
    I'm pretty sure I managed to OC my 6970M from 680/900 to 750/1050
    I used MSI Afterburner to save the modified bios then used ATIFlash 274 to flash the card (version 284 wouldn't do the trick).
    [​IMG]

    Before doing all that I replaced the thermal paste with MX-4 and got better thermal pads on the memory chips + thermal pads on the adjacent MOSFETS as well.
    Also used thermal pads to stick a couple copper shins on the back of the card - not sure if it helps but I had those shins to spare so…
    And I have Macs Fan Control on OSX to take care of the temps - past 50C on the GPU and the fan starts to go faster. So far managed to keep temps between 50C-65C.

    The thing is: temps to indicate the OC was successful but is there a app similar to GPUZ I can use to verify the GPU's clocks under OSX?
    And I couldn't change the voltage at all, does it means I missed something or this particular card doesn't allow voltage mods?

    Here's the modded bios I used if anyone's interested (you'll have to change the extension to 'rom' - no quotes):
     

    Attached Files:

  15. h9826790, Sep 12, 2018
    Last edited: Sep 12, 2018

    h9826790 macrumors G4

    h9826790

    Joined:
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    Hong Kong
    #15
    You mean you OC the GPU in afterburner? Then save the VBIOS?

    Or you use another way to mod the dump VBIOS?

    For me, it looks like you only OC the card in Windows (via Afterburner), then dump the ROM.

    If this is true, then your ROM is NOT OCed.
    --- Post Merged, Sep 12, 2018 ---
    Not sure which OS version you use now. But you may try this in terminal

    Code:
    ioreg -l |grep \"PerformanceStatistics\" | cut -d '{' -f 2 | tr '|' ',' | tr -d '}' | tr ',' '\n'|grep 'Temp\|Fan\|%\|(W)\|Hz'
    to monitor the GPU parameter

    You can use this command in automator to monitor the GPU. e.g. I make it refresh every 2 seconds.
    total power.jpg
     
  16. caincha macrumors newbie

    caincha

    Joined:
    Jul 15, 2012
    #16
    Thanks for the reply :)

    I OCed under MSI Afterburner then used GPUZ to dump the bios and ATIFlash to flash the card.
    I use MacFansControl under OSX and it shows higher temps so I assumed it went ok.
    Then I tried something different just for kicks: underclock it to see what happens.
    And after that I only managed to get back to stock clocks, unable to OC again - ATIFlash says 'VBIOS already installed'… Bummer…

    Also it seems the vCore is locked, is it possible to change it on this card?
    The idea is to OC and undervolt slightly. Read somewhere else this might keep temps at bay…
     
  17. h9826790 macrumors G4

    h9826790

    Joined:
    Apr 3, 2014
    Location:
    Hong Kong
    #17
    The card won’t OC in MacOS because of that.

    That “higher temperature” most likely just a coincidence after your first attempt, not really because the GPU is OCed.

    Afterburner CANNOT alter the VBIOS. IF it can alter the VBIOS, when a user accidentally set some "wrong" (or extreme) parameter cause a crash, the computer will never able to boot again (because those "wrong" parameter already written into the VBIOS, and the GPU will go direct back to that "crash state" on the next boot. Therefore, Afterburner won't (and cannot) write the VBIOS.

    So, as long as it won't alter the VBIOS, no matter what you set in Afterburner. When you dump the ROM, you are always dumping the original unmodded VBIOS.

    I OCed my GPU in macOS quite a few times, but only on the Mac Pro because it can use standard PC graphic cards, very easy to replace. Also, some cards like 7950 has dual ROM design, make it fail safe for flashing.

    I fact, I made a post about how to OC / undervolt the RX580 not long ago.

    https://forums.macrumors.com/threads/sapphire-pulse-rx580-8gb-vbios-study.2133607/

    Technically, you can do the same thing on the iMac. However, you need to have

    1) an associated VBIOS editor (or you know exactly how to mod the ROM in Hex editor)
    2) a graphic card that the ROM is NOT locked

    And each requirement has its own issue here.

    1) we don't know if those VBIOS editor can edit a Mac graphic card's VBIOS properly or not. I am not familiar with the iMac GPU, but AFAIK, 6790M is still using EFI UGA driver to display the boot screen. If the Radeon BIOS Editor can't handle that and disable / corrupt the EFI part without telling you anything. You may end up brick the card or even the whole iMac (because the iMac try to initialise the graphic card with some corrupted data), or lost the boot screen (this is no big deal, you can always flash the original ROM back in).

    2) technically, as long as you can mod the ROM in a Hex editor, any ROM can be modded, and any lock can only lock your card at the newly modded voltage. HOWEVER, if the ROM is locked, then how can you test the setting before you flash the card? To flash a GPU (especially this kind of old GPU), we need to run lots of benchmarks, stress tests to confirm the setting is stable / safe before we write it into the VBIOS. If the voltage is locked, you have no way to test it, which also means it's totally unsafe to mod the VBIOS voltage table.
     
  18. caincha macrumors newbie

    caincha

    Joined:
    Jul 15, 2012
    #18
    I’ve found the bios for the same card but the 2gb version and ATIflash changed the bios easily.
    Also found the previous version of the original bios and again it was easy to change with ATIflash - but this time I got artifacts so I reversed it back to original bios.

    The thing about MSI Afterburner makes sense thanks for pointing that out :)
    I have no idea how to hex edit anything so I’ll either try to find a modded bios from a reliable source (yeah good luck with that lol) or just leave it alone...
     

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