what does having more vram do?

Discussion in 'Mac Pro' started by alienex, Feb 16, 2006.

  1. alienex macrumors regular

    Feb 11, 2005
    what does having more vram do and benefit you?
  2. Mr_Brightside_@ macrumors 68030


    Sep 23, 2005
    better graphics= cooler effects. some video games call for higher graphics and will say that in their req's. for example, if you have ever seen the Cube effect, either in Keynote or when switching users, it requires 32MB VRAM- it works on my iBook gg w/ 32MB but not on my old iBook w/ MB. basically, more VRAM= more $ but better effects. hope that helps you!
  3. AJBMatrix macrumors 6502


    Feb 6, 2006
    Athens, Georgia
    It gives better response when playing games. It will be used in high end video editing. I also think it will be more important in future OS upgrades considering that OSX uses a small amount of VRAM but the future will most likely have more demanding graphics. This is also something that cannot be easily upgraded in the future and is best done from the factory. These are the reasons that I decided to upgrade.
  4. SmurfBoxMasta macrumors 65816


    Nov 24, 2005
    I'm only really here at night.

    On iMacs & lappys, your statement is correct, but not on mac towers, where upgrading is as easy as removing 1 card & installing a new one with more vram, then selling the old one to get back some of the $$ spent on the new card :)

    But to the OP, having more vram enables higher display resolutions, allows for having more application windows open at once, faster screen redraws/resizing, and in the case of 3D stuff like games & modeling, makes transistions, effects and real-time editing smoother & faster. Among other things :)
  5. jhu macrumors 6502a


    Apr 4, 2004
    if you don't play games, not much. games store textures in vram for faster access. for a windowing environment it depends
  6. radiantm3 macrumors 65816


    Oct 16, 2005
    San Jose, CA
    It improves response and effects in OS X a lot. Going from 64meg to 256megs made exposé a lot smoother, and 1080p HD content went from about 10-15fps to full frames (is that 24 or 30fps??). Those were the most noticeable differences besides in 3D graphics.
  7. Thomas Harte macrumors 6502

    Nov 30, 2005
    The OS X drawing path completely separates window composition from redraw. That's why even non-responding apps do not end up with trails in their window space unlike on Microsoft Windows.

    One of the things it does to help achieve this is to keep a pixel copy of the current contents of every window in memory. When the window changes its contents, that buffer is updated. Any time the window needs to be drawn to the screen the contents of that buffer are used.

    Since 10.2 we've had Quartz Extreme, which moves the compositing onto the video card. So it is responsible for taking the various window buffers and combining them all to make the desktop. Of course it does that by referencing the various textures one at a time, in turn.

    If you have "enough" video memory then all your open apps are able to permanently keep their window contents buffers in VRAM and all desktop redraw tasks are nice and smooth - including Expose and Dashboard tasks.

    If you do not have "enough" video memory then the window contents buffers must be swapped in and out of VRAM as and when they are needed. I'm not 100% sure how OS X 10.2 deals with that, but certainly on 10.3 and above VRAM is virtualised in much the same way as main memory is. When apps allocate more memory than you have in physical RAM the system uses the hard disk to swap bits in and out. When everything wants more VRAM than is available, parts have to be swapped from there in and out of RAM.

    That costs time and makes the system slower.

    That said, even without knowing the exactities of pixel format and how cards handle memory allocation for non-power-of-2 textures, you have to be going some to fill up even most of the low end cards.

    Supposing you have a 1440x900 pixel display (the current low end iMac, I have no idea what a likely average would be as I'm not an obsessive follower of models and revisions and so on), even a 32bpp buffer as large as the whole screen should take only around 5 mb. So if you had a 64 mb card then you'd lose about 10 mb for the display, which I believe uses two buffers to ensure smooth drawing, and then be able to simultaneously run around 10 apps that had windows expanded to fill the whole screen hopefully without the OS having to do any significant shuffling back and forth between VRAM and ordinary RAM.

    In addition, any running OpenGL app may arbitrarily try to use as many textures as it wants, which will also go into the VRAM virtualisation scheme. Many apps that you wouldn't necessrily think are using OpenGL may do so, especially where they are doing quite a lot of their own geometric drawing rather than being mostly widget based.

    Image manipulation programs are another big eater of VRAM space - including Photoshop, anything based on Core Image or Core Video and presumably also Quicktime judging by the comments of radiantm3.

    OS X 10.4 includes a new feature, Quartz 2d Extreme (i.e. with an added "2d" in the middle) that on cards that support the OpenGL ARB fragment shader extension - in practice a GeForceFX, Radeon 9500 or better - allows a large proportion of window content drawing to be done on the graphics card. The feature is currently disabled by default, and so is presumably either not complete or not stable but it gives an idea of where things will head in the future. That should allow much greater redraw speeds but again will eat more video memory.

    Professionals also like to use multiple screens. That obviously eats further video memory.

    Amongst the current GUI providers, Apple are at the forefront of using the GPU to help with ordinary user interaction. Microsoft currently don't use the GPU at all, but Vista seems to do much the same stuff as OS X based on preview columns that I have read. In the UNIX world the next release of X.Org, the newish de facto standard for X-Windows servers in free UNIXs after a rapid fall from grace for XFree86, supports a suitable GL based drawing path extension that is hooked by KDE4 to do much the same thing.

    That all said, my Powerbook has 16 mb VRAM and as an undemanding user I rarely see any slow down from Quarz Extreme. I tend to run a browser, maybe a couple of Finder windows and XCode simultaneously and all Expose actions and other window manipulation tasks remain smooth the whole time - with the obvious exception of window resizing which is never smooth. If I plug in a second monitor I seem to lose Quartz Extreme judging by the sudden drop in overall smoothness.
  8. FarSide macrumors member


    Feb 16, 2006
    VRAM is for sure not the most important thing on a graphicscard. If you compare for example 2 Nvidia Geforce 7800 GTX [256/512], the larger will have a minimal advantage even at highest settings. Games don't need a larger buffer then 256MB at the moment, which is standard. But 256MB on a ATI Radaon X1600 [128-bit 4-channel GDDR3] is not the same as on a NVidia Geforce 7800GT [256-bit 8-channel GDDR3] and in the end, it's all about the GPU itself.

    That's the reason, why the ATI Radeon X1600 [PCI-E] is no match for an "old" ATI X800XT [AGP 8x] even they have same size of VRAM...

  9. MacSA macrumors 68000


    Jun 4, 2003
    Would you notice any difference when using a Mini with the 32mb 9200 card vs the 64mb on in the updated models?
  10. robbieduncan Moderator emeritus


    Jul 24, 2002
    Depends on a lot of factors, some of which are below:

    1) Size of screen. A bigger screen will require a larger frame buffer. This will leave less of the vram available for
    2) Number and size of open windows. All open windows have 2 buffers to enable flicker free drawing and animation. Lots of large open windows will eat into your vram. When you run out normal system RAM will be used but this will slow things down as data will be swapped in and out of vram almost all the time bogging down the memory bus.
    3) CoreImage effects. If any CoreImage effects are running on the GPU as opposed to the CPU they will require some vram for the source/target images.

    If you are just browsing the web etc with 10-15 open windows (across all apps) on a "normal" sized screen (say 1600x1200 max) then you will not notice much difference. If you use a higher resolution screen, have lots of open windows etc more vram is great.
  11. UberMac macrumors 6502

    Jan 5, 2005
    Yep! You need 64Mb for CoreImage (Ripples on widgets etc). I'm sure with Leopard (and onward) more and more features will require it so I think there is a big difference.

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