24" iMac - Bigger Screen wants more RAM?

Discussion in 'Buying Tips and Advice' started by netdog, Sep 7, 2006.

  1. netdog macrumors 603


    Feb 6, 2006
    I have been absolutely fine with 128MB on my 20" iMac Yonah, but does a bigger screen need more VRAM? Will I be sorry if I get the 24" with 128MB?
  2. neonblue2 macrumors 6502a

    Aug 25, 2006
    Port Pirie, South Australia
    You mean VRAM not RAM. But no it shouldn't make a difference.
  3. DeSnousa macrumors 68000


    Jan 20, 2005
    Brisbane, Australia
    That's what he asked :p

    It is fine, but it would be nice. It also really depends on what you use the computer for i.e. games, motion.app, etc
  4. Scarlet Fever macrumors 68040

    Scarlet Fever

    Jul 22, 2005
    more vram

    It looks like new features of X and XP are taxing more and more on the GPU. It doesn't cost a lot to double your VRAM, so i would recommend the 256 just for future proofing purposes.
  5. robbieduncan Moderator emeritus


    Jul 24, 2002
    With a larger screen you are likely to have more windows open, and larges sized (in terms of pixels) windows open. Each window is double buffered in main RAM and single buffered in VRAM to use the Quartz Extreme compositor. If you ever end up with so many windows that you run out of VRAM the OS will have to page windows in and out of VRAM to composite them. This is bad.

    A window takes width*height*4 bytes of buffer space to store so a 100x100 window requires around 40Kb of VRAM for it's buffer in the compositor. This ignores the shadows around windows so it's probably double that with shadows.

    The 24" iMac has a resolution of 1920x1200 so a single full-screen window requires 9000Kb or 8.8Mb of buffer. If we double that for shadows then we see that a single full screen sized window requires somewhere around 15Mb of VRAM. So with 128Mb of VRAM you will only get around 7 or 8 full sized windows in there (as you need to reserve a couple of full screen sized chunks for frame buffer and so on and shadows probably don't cost you as much as I'm allowing for).

    If Quartz 2D Extreme ever gets turned on (where all compositing within the window and drawing of everything on screen at a low level is done on the GPU not the CPU) then even more VRAM will be required.

    My recomendation: get 256Mb. It can't hurt.
  6. aswitcher macrumors 603


    Oct 8, 2003
    Canberra OZ
    256MB is a small % of the TCO now, and its unlikely Apple have made it upgradable. Leopard should switch on even more graphcis - and you may want to attach a second screen which again bumps the price up.
  7. SpaceMagic macrumors 68000


    Oct 26, 2003
    Cardiff, Wales
    The new iMacs are worth every penny in my opinion. I'd spend an extra 2pennies making it 256mb ram. Future proofing :D
  8. FFTT macrumors 68030


    Apr 17, 2004
    A Stoned Throw From Ground Zero
    I'm pushing my Dell 24" with 64 MB VRAM, so 128MB would be fine
    for anything short of intensive graphics and 3D.

    If you can afford the 256MB upgrade without too much trouble, go for it, but make sure you have enough left over to equip your new machine with at least 2 GB RAM.
  9. combatcolin macrumors 68020


    Oct 24, 2004
    Northants, UK
    Did the same with my old 64MB 8500 on my PC.

    And you can run 1920 *1200 with a 32MB card.

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