How does OS X (Snow Leopard) allocate video ram?

Discussion in 'macOS' started by lssmit02, Sep 21, 2010.

  1. lssmit02 macrumors 6502

    Mar 25, 2004
    I have a dual monitor setup on my mac pro. I didn't like having my second monitor on when I was running games, so I installed SwitchResX, which allows me to deactivate my second monitor. Does anyone know if this frees up video memory for the game?

    I emailed the creator of the program, and asked him if he knew if this would free up video ram for my other programs, but he did not know. He said that this would release the frame buffer, but wasn't sure if this meant that all of the card's video ram was released to handle the one monitor. I am skeptical that it does, because the system profiler still sees the second monitor, and says that it is online.
  2. x0r-lord macrumors member

    Aug 31, 2010
    Ottawa, Canada
    the Video RAM is allocated by the EFI.
    the only way to change the amount of memory allocated to VRAM is by changing the EFI settings, or possibly the firmware settings (possibly on nvidia chipsets).
    either way, if you had to ask, you shouldn't try.
  3. lssmit02 thread starter macrumors 6502

    Mar 25, 2004
    That means the only way to allocate all the video ram to one monitor is to unplug the second before booting, right? Well, at least SwitchResX allows me to shut off the second monitor so it's blank while I game. Most of the time, its great having two monitors.

    Thanks for the info.
  4. maflynn Moderator


    Staff Member

    May 3, 2009
    There's no way to allocate vram to a specific monitor, and nor should you care how video memory is being used. It's one of those black box things that we really don't need to delve into.
  5. lssmit02 thread starter macrumors 6502

    Mar 25, 2004
    Fair enough. I was just curious. I find it interesting that there is no easily accessible answer.
  6. Inconsequential macrumors 68000

    Sep 12, 2007
    Only just recently had programs reporting the VRAM usage in Windows.

    On the whole it's pointless as an empty 2D window uses a few MB at best, and if you've filled your VRAM then you aint got enough, simple as :p
  7. x0r-lord macrumors member

    Aug 31, 2010
    Ottawa, Canada
    The thing is, that with a dedicated card like yours, you don't want to interfere with the addressing of the vram, because you'd probably wreck the performance scalability.

    In order to increase the memory you would have to actually unsolder memory chips, and replace them. you would also have to write a new firmware for the card to allow for the new address allocation. (BASc. Electrical Engineering req'd)

    btw, system profile doesn't seem to accurately update the display information...

    heres a picture of my system profiler under graphics/display and my dedicated 330M, it says no display connected. I have a 24" connected at 1920x1200. this is a screenshot of it...

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