11 Replies Latest reply: Feb 23, 2008 7:57 AM by AlexDavis
Catholic OS Level 1 Level 1 (0 points)
I know that this question has already been posted here, but never satisfactorily answered. I have a Mac Pro with 4 GB RAM, running OS X 10.5, and Vista in Boot Camp. Yet Vista "sees "only 2 GB RAM. I also have a regular PC box (Dell XPS), also running Vista, which "sees" 4 GB RAM without any problems.
Does anybody know if Apple placed a limit in the BIOS so that Boot Camp can only use 2 GB, or is there something else?

Mac Pro 4x2.66, Mac OS X (10.5), 4 GB RAM, 1.5 TB HD's
  • ChrisF Level 1 Level 1 (125 points)
    I have a similar setup to yours. My install of 32 bit Vista business sees only 2 GB of the 3 GB installed RAM. The only way around this, to my knowledge, is to install a 64 bit flavor of Vista, but then the appropriate 64 bit drivers have to be located and installed - Intel chipset, video, audio, network, etc.
  • Marcos Scriven Level 1 Level 1 (0 points)
    This gets asked a lot, and a Google search yields plenty of info.

    Here's a link for you:


    I doubt very much that only 2gb is showing, unless one of the sticks simply isn't working. Does it show up ok in OS X? As per the link above, you'll have somewhere between 2.5 and 3.5 GB. I would think around 3gb should show up.
  • squier Level 1 Level 1 (0 points)
    I can confirm this, in bootcamp XP the MacPros in our lab only show 2 gigs even though they have 4 installed.
  • Rubberneck Level 1 Level 1 (30 points)
    There are other threads on this topic, I was under the impression that this was a Mac Pro specific problem. I also have 4gb, with only 2gb showing in XP 32. It seems bootcamp just isn't allowing all 4 to be accessed...
  • James Bond 007 Level 6 Level 6 (16,975 points)
    We don't know, but I think this is a hardware limitation, perhaps in the chipset.

    In the PC side, older Intel chipsets such as 945 or below (as far as I know) cannot see more than about 3GB of RAM when you are using a 32 bit version of Windows. For newer chipsets such as 965 and P35 you can see about 3.5GB and if you are using a 64 bit version of Windows, you can see the full 4GB RAM for these new chipsets.

  • Jeronimo Colon Level 1 Level 1 (0 points)
    There's a lot of misinformation floating around about the 4GB limit, in general, with regard to Windows. It's confusing enough for Windows savvy people - add in Mac savvy (but potentially Windows novices - not that all are) trying to understand why they can't see all their installed RAM and even more misinformation gets circulated.

    I'm a Windows developer and we have a very memory intensive finacial application at work that we wrote and I was tasked with researching Windows' memory architecture and any potential there might be to tap more memory above the 4GB (2/3GB working set i.e., non-kernel) limit using things like address extensions. I've written a lengthy report about my findings for my manager. Most of it is too esoteric for a general audience but I'll post the gist of it. Also, I have accumulated tons of reliable and authoritative bookmarks I've on the subject. Unfortunately I'm currently on vacation and all my hard research is at work but when I return to my office I'll update this post with the relevant bookmarks.

    Here's the nitty gritty:
    - The Windows operating system, itself, can fully address 4GB of RAM. No if and or buts about it.
    - The limiting factor, believe it or not, is the machine's hardware coupled with the chipset it is using.
    - Without too much technical detail - it boils down to certain pieces of hardware having to borrow memory from the upper levels of your address space to use for its own addressing. So basically the more devices you have installed, internally, the more potential there will be for loss of addressable memory. Please keep in mind not all device "steal" memory for addressing purposes. Don't worry I'll post a link about this.

    With that said, I believe in the case of Boot Camp, it might be a combination of Boot Camp not making the full amount of RAM available when it does it's BIOS emulation magic and internal devices, namely the PCI Express bus and attached peripherals, stealing RAM for it's addressing, but I need to do more research about that. The more cynical hypothesis would be that Apple is purposefully crippling Boot Camp's addressable memory limit - let's hope that's not the case. What I can say, though it's not nearly apples-to-apples so to speak, is that I can run Vista in VMWare and seem a lot more than 2GB of RAM.

    The reality is that Apple needs to just come out and speak frankly/clearly/whatever about why we can only see 2GB of RAM when using boot Camp as well as if they plan on addressing it (if they can). Way too many people are confused about this to stay silent and this has been a hot topic since Boot Camp was in beta. I'm a switcher and the only thing I use Windows for (through Boot Camp) is Visual Studio and that's only if I take work home. My whole world now revolves around Macs I've adopted all my tasks and interest to be down through OS X but I will say that getting to the nitty gritty about things in OS X land feels like pulling teeth sometimes. That's probably the only thing I feel Apple needs to improve on and unless they've posted something recently that I've missed I doubt they will ever be forthcoming about our Boot Camp memory concerns. Let's hope they prove me wrong...
  • bongoherbert Level 1 Level 1 (10 points)
    In the 'for what it's worth' category-

    I have two MacPros w/ 8GB of RAM. Each only shows 2GB in XP (32bit).
    I have a MacBook Pro w/ 3GB of RAM. It shows 3GB in XP.
    My iMac has 2GB and shows 2GB.
  • Rubberneck Level 1 Level 1 (30 points)
    Can anyone with Leopard weigh in on this? (long shot, but ya never know!)
  • bongoherbert Level 1 Level 1 (10 points)
    Not quite sure what you mean there re: Leopard but in my case at least, all machines are running Leopard / using the 'official' release of boot camp. I would bet many of the folks seeing this are too.
  • bongoherbert Level 1 Level 1 (10 points)
    Turns out, Vista x64 installs fine on my MacPro, sees all 8GB. There are some 64bit drivers available on the Leopard DVD, the chipset driver I got right from Intel, the ATI driver from ATI.

    My Vista x32 only saw 2GB like many others report here. So... for now, its Vista x64...
  • AlexDavis Level 1 Level 1 (0 points)
    Are you using Bootcamp to install Vista x64?