Memory not being identified in XP

Discussion in 'Mac Pro' started by wsgroves, Sep 19, 2006.

  1. wsgroves macrumors member

    Sep 19, 2006
    Hi guys. I just threw in 2 more gigs into my mac pro bringing the total to 3 gigs. 2x1 gig sticks and 2x 512meg sticks. Interesting thing is, windows only reports 2 gigs installed. I run sandra to test things and it reports 4 dimms installed in windows and quad channel memory mode is active. OSX reports 3 gigs correctly. Anyone else seen this prob? Thanks

  2. trogdor! macrumors regular

    Mar 7, 2006
    xp only supports 2gigs if im not mistaken, so only 2gigs will show up.
  3. wsgroves thread starter macrumors member

    Sep 19, 2006
    Thanks for the reply. XP allows up to 4 gigs I believe though.


    booted off a live linux cd and it only sees 2 gigs also.........
  4. slughead macrumors 68030


    Apr 28, 2004
    WOW! I just dropped in to ask the same question:

    I have 3GB in my machine, but lookey:

  5. suneohair macrumors 68020


    Aug 27, 2006
    If i does it in Linux too, I would imagine Windows and Linux just don't see one riser.

    Did you try putting all the sticks on the same riser? Switching them around, etc?
  6. wsgroves thread starter macrumors member

    Sep 19, 2006
    Yes I have tried them on one riser and switched them around with still the same outcome. =/ It driving me nuts lol.
  7. suneohair macrumors 68020


    Aug 27, 2006
    Hmm. So Windows and Linux default to the riser with the most RAM. Maybe that is the EFI taking over to limit the amount of RAM used in Windows and Linux?

    I know that Windows has a memory whole at 3GB, but I didnt think it would just act that a whole GB isnt there.

    Is this happening in x64?
  8. wsgroves thread starter macrumors member

    Sep 19, 2006
    No its x32. I tell ya if they somehow limited it to a certain amount you could run in windows im sure myself and alot of people will be not too happy =/
  9. wsgroves thread starter macrumors member

    Sep 19, 2006
    I just got this reply in apples forum - from Ned Snowing

    This is normal. While there is a reason for it (unfortunately I don't know it although someone surely does) XP is not able to identify more than 2GB RAM in the Mac Pro.

    You are not alone in this.

    You have got to be kidding me....
  10. suneohair macrumors 68020


    Aug 27, 2006
    I doubt this is an Apple problem. I am guessing it deals with EFI.

    Maybe we should try and get someone with an iMac that has 3GBs. Have them install Windows and see what happens.
  11. wsgroves thread starter macrumors member

    Sep 19, 2006
    Another update....just installed Vista RC1 x32.
    Same problem, only 2 gigs showing up.
  12. stealiesubee macrumors newbie

    Aug 26, 2006
    Fixed with Firmware update

    I updated my EFI firmware and it now reports 2.98gb of RAM in WinXP x64.

    Prior to my update it would only report 2gb as many have stated, but Photoshop CS2 was able to see all of the memory and I was able to allocate more than 2gigs to CS2.

  13. slughead macrumors 68030


    Apr 28, 2004
    I applied the EFI and SMC updates and experienced no change... It wouldn't make much sense for either to have an effect, but I tried anyway because of what the previous poster said.

    Still 1.98 gigs of RAM shown out of a total of 3GB.

  14. wsgroves thread starter macrumors member

    Sep 19, 2006
    Interesting. MAybe it is a problem with the 32 bit os'es? I dont have a 64 bit version to install to test . Maybe another person with the problem can install one and see if that fixes it?
  15. sirnh macrumors regular

    Aug 16, 2006
    I only have 2GB installed in my system. Actually, I believe that unless you are doing a lot of photo work for print or HD video editing, running a large corp database, or need to dozens of programs running at once, more than 2GB is overkill.

    But, there are ways to make Win XP see more than 2GB of RAM. You need to modify your C:\boot.ini file, to do so.

    In your boot.ini you will find an [operating systems] section. I recommend taking the boot entry you normally use there (most users will only ever see one entry) and duplicating it. Next, you need to modify one of the two duplicate entries. If you want to default with more than 2GB at start up, modify the top-most of the duplicates.

    You need to add /3GB /userva=<number> where <number> is equal to the amount of RAM you want visible to the OS measured in megabytes. This number should not extend beyond 3072 (3GB).

    Increasing this number allows processes to have more virtual address space, but takes address space away from the kernel. Windows normally reserves the upper 2GB of virtual address space for kernel use. By taking address space away from the kernel, you may create problems with the kernel. Errors like blue screens may occur if you increase this number too much. We use a /userva value of 2500 or 2700 with our products.

    I strongly recommend that you back up your boot.ini file, and that you make all modifications CAREFULLY. An improper boot.ini may leave your system unbootable.

    Below is an example boot.ini file:

    [boot loader]
    [operating systems]
    multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional 2.5GB" /3GB /userva=2500 /noexecute=optin /fastdetect
    multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional" /noexecute=optin /fastdetect
  16. EricTheRed71 macrumors member

    Sep 15, 2006
    I'm sorry but that's not really correct.

    The "3GB switch" as it is know is not to allow the PC to see more than 2GB of RAM, it can see up to 4GB anyway. The switch is needed to allow XP to use more than 2GB for a single process. The "userva" part is if you experience instability as it allows you to specify exactly how much RAM can be assigned to a single process.

    It has absolutely nothing to do with the RAM problem on the Mac Pro. The fact that the latest firmware upgrade solved this problem if you are using XP64 proves that the problem lies at Apple's door.

    I happen to agree with you actually that more than 2GB is usually wasted in XP, due to the 2GB per process limit but where it got frustrating was when you want to install XP64 which could take advantage of a theoretical 16GB in the Mac Pro.
  17. wsgroves thread starter macrumors member

    Sep 19, 2006
    Ok I just installed XP 64bit trial and can confirm it DOES see my 3 gigs now.
  18. sirnh macrumors regular

    Aug 16, 2006

    If you install more than 2GB of RAM inside a Win32 box, Windows will never report more than 2GB by default in the System control panel. This has been true on my hp development system, which has 3GB installed.

    And you are somewhat correct in saying that the /3GB affects the amount of memory available to a single process. Actually, what it affects is the user virtual address space (thus userva). This defines how much address space is reserved for ring 3 (user mode) processes.

    Before you discount my suggestion, you should give it a try. Comparing a Win64 solution to a Win 32 solution is not a valid comparison.
  19. aneks macrumors regular

    Aug 29, 2006
    not true, rmb on My Computer and choose 'Properties'

    the XP machines here display 3gb of ram (even without the /3gb line in the boot.ini) . however we are unable to make our mac pro's display more than 1.98 despite having 4gb installed on WinXP sp2. I beleive that under vista and win64 mac pro's will correctly show the ammount of ram.
  20. wsgroves thread starter macrumors member

    Sep 19, 2006
    It does not properly show under 32bit vista I tested it. It still only sees 1.98.

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