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32bit OS, new dual cards etc

Discussion in 'Nvidia' started by Thomas Andersson, Jul 24, 2009.

  1. Ok I guess this might be a daft question, but I've been wondering.

    With 32bit OSes and the 4GB limit on addressable memory, how does that work
    with these new fancy dual-gpu cards that can have almost 2GB of gfx ram on
    them. To the extreme, quad sli using those where they themself have almost
    4GB ram. Is this at all workable with 32bit XP ?
    Can someone please elaborate on this issue a bit?

    Thomas Andersson, Jul 24, 2009
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  2. Thomas Andersson

    deimos Guest

    In general you might get a BIOS screen, but if XP even boots, you'll be
    dealing with less addressable memory than the cards can actually use. I
    don't know of anyone who's ever tried this (4GB Quad SLI on 32-bit) and
    it just happens to be that when such technology became available; almost
    all review sites and enthusiasts would be using a 64-bit Vista

    If you look at raw memory allocation; your BIOS needs to remap
    everything via hardware (the mobo chipset) or a software implementation
    (BIOS) to make 4GB show up on POST. You're not using anything above 1MB
    at that point, so it's all hardware setup before the BIOS hands things
    off to the OS.

    At that point the OS takes over and handles addressing above 4GB. This
    is either a mode switch to 64-bit real mode (I believe that's what it's
    called) or a 32-bit protected mode where the OS has a hard coded limit
    of addressable memory (usually 3.5GB with all devices, Linux can get
    around this using some memory tricks with a "moving window" of addresses).

    Then you have to deal with the display driver, can it even use all that
    memory under 32-bit mode? Chances are no, and for some reason MS and NV
    only know.

    Besides, even with a 2GB video RAM configuration, the disproportionate
    balance between available texture memory and system memory to actually
    execute the game would likely just drown out any benefits.

    I noticed this on a small scale when I went from a 512MB card that
    allocated only 512MB in 32-bit under the BIOS to one that likes to give
    itself a full 1GB. Losing that .5GB pretty much nullified the extra
    fluidity I obtained with a little over 3GB in Crysis/Wars and was just
    one of the motivators I had to install 64-bit Vista.
    deimos, Jul 24, 2009
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  3. Thanks you for a good answer.
    Basically what it comes down to is that if you want to do anything fancy you
    more or less have to go 64.
    Which gives a follow up question. I know many gamers swear by XP still, but
    was is the optimal gaming OS today if you need to go 64bit (drivers/games
    performance vise). XP Pro, Vista or Windows 7 ?

    Best Wishes
    Thomas Andersson, Jul 25, 2009
  4. * deimos:
    Not only Linux. Windows Server (depending on the version) can do that as
    well, as can other operating systems like Solaris or Mac OS X.
    This is called "PAE".

    Benjamin Gawert, Jul 25, 2009
  5. * Thomas Andersson:
    No. Basically it comes down that except you don't really need 16bit
    application compatibility (which 64bit Windows doesn't have) or have
    certain hardware which you need and for which there are no 64bit drivers
    then there is no reason to go for a 32bit Windows any more.
    Right, but doesn't say much.
    Forget Windowsxp x64, it was never meant for the mainstream (it is
    basically a stripped-down Windows Server 2003 x64 aimed at the
    Workstation market), and it has limited driver support (which won't
    improve in the future). Vista x64 would be the way to go as it comes
    which much better driver support, however, no with Windows 7 being close
    to release I would just wait for that.

    Benjamin Gawert, Jul 25, 2009
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