Blue and White only seeing half of the RAM

Discussion in 'Mac Pro' started by Nermal, Aug 6, 2006.

  1. Nermal Moderator

    Nermal

    Staff Member

    Joined:
    Dec 7, 2002
    Location:
    New Zealand
    #1
    My B&W G3 has been running on 128 MB, so I just bought two 256 MB modules for it (to bring it up to 640 MB). However, the system is seeing each of the new modules as only 128 MB (for a total of 384 MB). I've reseated them and checked the labels, they're definitely 256 MB modules.

    Help! :eek:
     
  2. Quartz Extreme macrumors regular

    Quartz Extreme

    Joined:
    Jun 9, 2005
    Location:
    Outside of the box
    #2
    The Blue and White G3's memory controller only supports memory of a limited density.

    It will only read the first half of the higher density chips.

    I believe it works roughly like this:

    512MB card (Only sees 256MB)
    [32] [32] [32] [32] [32] [32] [32] [32] front
    [32] [32] [32] [32] [32] [32] [32] [32] back

    high density 256MB card (Only sees 128MB)
    [32] [32] [32] [32] [32] [32] [32] [32] front
    [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] back

    low density 256MB card (Works)
    [16] [16] [16] [16] [16] [16] [16] [16] front
    [16] [16] [16] [16] [16] [16] [16] [16] back

    high density 128MB card (Works)
    [16] [16] [16] [16] [16] [16] [16] [16] front
    [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] back

    low density 128MB card (Works)
    [8] [8] [8] [8] [8] [8] [8] [8] front
    [8] [8] [8] [8] [8] [8] [8] [8] back

    Macsales.com and DealRAM.com would be good places to look for compatible modules.
     
  3. Nermal thread starter Moderator

    Nermal

    Staff Member

    Joined:
    Dec 7, 2002
    Location:
    New Zealand
    #3
    Ugh. I've just emailed the place I bought it from to see whether they can get me double-sided modules. In the meantime it looks like I'll have to find someone to sell this single-sided stuff to.
     

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