3GB switch in Win XP

Discussion in 'Mac Pro' started by damado, Nov 11, 2006.

  1. macrumors 6502

    Aug 8, 2006
    Has anyone had luck with enabling 3GB RAM in win xp?

    I put

    multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional 3GB" /fastdetect /3GB
    multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional" /fastdetect

    in my boot.ini and chose to boot with the 3gb and it still shows 1.98 gb in the system properties.
  2. macrumors newbie

    Nov 10, 2006
    Northern Cali
    You need to add the switch /PAE as well.
  3. MRU
    macrumors demi-god


    Aug 23, 2005
    ok can someone post in the exact thing I need to copy & paste into the ini file and i'll give this a try too.

    Does it actually enable 3gb or force it just display 3gb in the system profiler?
  4. thread starter macrumors 6502

    Aug 8, 2006
    Bub thanks, but it's still displaying 1.98 GB. Although it now shows physical address extention under it. Do I need 4 gigs for this or just 3 gigs to make it work?
  5. thread starter macrumors 6502

    Aug 8, 2006
    Should just be
    multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional 3GB" /fastdetect /PAE /3GB
  6. macrumors 6502a

    Aug 30, 2006
    Are there any drawbacks to doing this, or is it just Microsoft being totally random and unhelpful?
  7. macrumors newbie

    Nov 11, 2006
    The /3GB switch has nothing to do with the amount of physical memory in the machine. What it does is change the VM split from 2/2 to 3/1 so that Windows will allow each process up to 3G of VM and only allow the kernel 1G. And Windows only allows a process 3G of VM if the executable is marked "large address aware" because a lot of apps will crash if given addresses >2G, some executables like SQL Server should be marked already and there's a tool in the resource kit that lets you mark executables yourself but you're better off getting a 64-bit version of the executable if one exists.

    Also PAE is required for a 32-bit OS to get access to >4G of memory but it has no affect on XP or Win2K because they're artificially limited to 4G by MS. All PAE does in XP is enable the NX stuff. You'll need a 64-bit OS or Win2K3 Server to get access to all of the memory.

    Most likely the OP's problem is hardware resources taking up over 2G of addresses. If you have SLI take out on of the cards and see if the amount of memory that Windows sees changes, if you don't have SLI try a video card with less memory.
  8. thread starter macrumors 6502

    Aug 8, 2006
    Thanks for the responses. I don't really want to take out the X1900XT I have in there. I tried the PAE and 3GB switches and noticed that the computer started to stutter a bit sometimes when I was running EQ2 windowed, esp when switching to firefox. I undid the switches and no more stutter. oh well =(
  9. macrumors 65816

    Nov 6, 2006
    Norfolk, UK
    right im running xp pro 32bit sp2 with an opteron 175 and 4gb of ram

    my boot.ini is as below

    My graphics is currently onboard so takes 256mb of the ram away and I see 3gb of ram (minus the 256)
  10. macrumors newbie

    Nov 11, 2006
    And I'll bet that if you remove the /3GB switch you'll still see the exact same amount of memory.
  11. macrumors 65816

    Nov 6, 2006
    Norfolk, UK
    Actually I only see 2gigs (i know because it was annoying when I first installed xp on this system), pae is automatically enabled in any x64 cpu since sp1 iirc, hence the reason it isnt in my boot.ini
  12. macrumors newbie

    Nov 11, 2006
    PAE in XP is only for the NX stuff, since 32-bit XP is limited to 4G of memory by MS it has no effect on how much memory the OS can use.
  13. macrumors regular

    Aug 29, 2006
    No one has managed to prove to me that you can get a mac pro to see more than 1.98gb of RAM in windows xp 32bit. I am running exactly the same line that allow me to see 3.37 gb of ram on my windows box but sorry kids no go !

    I beleive that this is a none issue and that folks are balming the way the daughter board/ ram risers are working on this system
  14. macrumors 68030


    Apr 28, 2004
    spelling is thine enemy

    maybe they'll be able to hack it in a firmware update
  15. macrumors newbie

    Nov 11, 2006
    The motherboard resources on your Windows box obviously take up less address space than those on the Mac then because that's what makes the memory unaddressable. Onboard resources and add-in cards all need memory ranges so that the OS can talk to them and the more you have of them the more addresses are stolen from that 4G range. Also if XP wasn't artificially limited to 4G by MS this wouldn't be an issue, installing a copy of Win2K3 Server which allows you to use to up 8G of memory will prove this.

    It's possible that the daugherboard and memory risers take up some of that address space, but the latter definitely seems unlikely and I haven't poked around in my friend's MacPro to find out.
  16. macrumors newbie

    Sep 10, 2006
    1.98GB RAM in Windows XP

    To answer damago and aneks, I believe the reason XP 32-bit version will not show us more than 1.98Gigs of ram has something to do with boot-camp if this is in fact how you run Windows (don't know much about ram support in other methods such as virtual pc or parallels). Again I am only assuming that you are because I see the exact same thing when I'm running XP on my mac pro.
    I recently purchased an additional 2gigs of ram from macramdirect.com which would place me at 3gigs. Right from the start I made sure I had installed them (2 x 1gig) correctly and OS X had no problem reading all 3gigs. Windows, on the other hand, would not. I've tried rearranging the original gig (2 x 512mb) into the second pair of slots and placing the the new (2 x 1gigs) into the first pair and vice versa, with no luck. Still says 1.98gigs.
    I've tried the /pae and /3gb switches in the boot.ini file and still no luck.
    I tried contacting macramdirect's tech support and they swear that it has something to do with boot camp since it is still in the beta stages. They have heard this problem again and again and claim that they cannot help me any further because their memory is guaranteed to work with macs (or in this case, OS X and not Windows).
    This sounds like something that will be resolved over time, maybe when boot camp reaches a closer-to-final stage.

    Boards and Risers? Sounds like some people haven't tried and succeeded installing more ram in a mac pro running xp 32-bit. The more immediate issue looks to me like it has a lot more to do with the fact that apple has not perfected the available utilities to make the full shift work.
  17. thread starter macrumors 6502

    Aug 8, 2006
    Thanks for the responses, I don't use bootcamp tho. I installed windows by itself on it's own HD. I just select which OS I want to boot into through the restart option in each OS.
  18. macrumors newbie

    Sep 10, 2006
    Maybe in the next firmware update?

    Perhaps this issue will be addressed in the next major firmware update, whenever that is... Let me know if anyone finds a solution for this I would really appreciate anything.


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