Mac Pro not recognizing memory properly

Discussion in 'Mac Pro' started by Egomaniac, Aug 25, 2006.

  1. Egomaniac macrumors newbie

    Joined:
    Aug 9, 2006
    #1
    I bought my mac pro with the stock 1GB of memory, and bought another 2GB (2 x 1GB sticks) from OWC to upgrade it with.

    The extra memory just got here. I pulled out the second riser board, added the two extra RAM sticks on the back two slots, and booted my Mac up. And presto! Instead of 1GB, "About This Mac" now shows that I have... 2GB. Frankly, I had rather expected that taking a 1GB machine and adding an extra 2GB would yield a 3GB machine.

    Something is definitely fishy. I swapped the two memory riser boards. No change. I pulled out the original 1GB of memory and left just the 2GB I had added... and it worked fine, showing 2GB of total memory. I added the original 1GB back and it stubbornly remained at 2GB. I checked the System Profiler and it properly shows all four memory sticks, totalling 3GB of memory. But everywhere else in the system it says I only have 2GB.

    Can anyone explain just what the heck is going on here? Am I not allowed to mix-and-match memory sizes like this?
     
  2. CrackedButter macrumors 68040

    CrackedButter

    Joined:
    Jan 15, 2003
    Location:
    51st State of America
    #2
    From what I heard on the net you have to install them in pairs. I could be wrong as I don't own a MacPro.
     
  3. MacProDude macrumors member

    Joined:
    Aug 16, 2006
    Location:
    SF Bay Area, CA
    #3
    He indicates that he is installing them in pairs.

    I have the same config: Mac Pro 2x512MB Apple and 2x1GB OWC. No problem here.
     
  4. CrackedButter macrumors 68040

    CrackedButter

    Joined:
    Jan 15, 2003
    Location:
    51st State of America
    #4
    I read it wrong, I thought he had 3x1GB modules. Sorry.
     
  5. macenforcer macrumors 65816

    macenforcer

    Joined:
    Jun 9, 2004
    Location:
    Colorado
    #5
    Pull out all the ram and re-seat it properly. Happened to me. Also make sure you install 2 in the bottom back and 2 in the top back. That is the config.
     
  6. Egomaniac thread starter macrumors newbie

    Joined:
    Aug 9, 2006
    #6
    Figured it out, and yes, I'm a dumbass.

    In order to get Parallels working on the Mac Pro, I had used the suggested workaround of 'sudo nvram boot-args="-legacy maxmem 2048"'. Given that the "maxmem 2048" was necessary for Parallels to function even when my system only had 1GB of total RAM, I assumed it setting the size of the per-process address space or something along those lines. It obviously has to be doing something other than just controlling the total system memory, or it wouldn't have made any difference with my paltry 1GB of RAM.

    But, lo and behold, I changed it to "maxmem 3072" and my system is now properly reporting all 3GB of RAM. So in addition to whatever else it is doing, that command does indeed limit the overall system memory. Whatever. I'm now happily running with 3GB.
     
  7. Darth Xena macrumors newbie

    Joined:
    Nov 11, 2007
    #7
    Hi I have a similar problem. I had 2 gigs in my MacPro and upgraded with 2 additional 1 gig sticks from OWC for a total of 4 gigs. For about a week, it recognized all 4 gigs just fine, and then today I notice it says I just have 3 gigs.... I am a total noob at this, what should I do?
     
  8. Darth Xena macrumors newbie

    Joined:
    Nov 11, 2007
    #8
    I reseated my memory risers and that fixed it.
     

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