Why Windows XP only given 2.75GB RAM on 18GB host?

Discussion in 'Windows Guest OS Discussion' started by DonLeckie, Jan 13, 2009.

  1. DonLeckie



    I have searched the knowledge base, all the documentation that I could find, and searched Google. But I found no answer.

    My Mac Pro has 18GB of RAM. Parallels & Virtual Machine memory is automatically controlled.

    My Virtual Machine has 8GB allocated to it.

    Windows XP dynamically controls the paging file size.

    When I look in the System dialog, the amount of memory recognized by Windows XP is only 2.75GB. I expect it to be 3.75GB since the Virtual Machine is 8GB.
    - How can I get that missing 1GB of Windows XP memory?
    - How much memory does the Virtual Machine need in addition to Windows XP?
    - Can I lower the Virtual Machine`s 8GB down to 5.5GB or 6GB and still have Windows XP with 3.75GB?

    I have Parallels Desktop for Mac 4, build number: 4.0.3810 (December 30, 2008).

    My Mac Pro ...
    Mac OS X 10.5.6 Leopard
    2 2.8GHz Xeon Processors (8 cores)
    18GB memory (yes, eighteen)
    1 360GB master drive
    3 1TB slave drives
    1 Super DVD/CD-ROM drive
    1 NVIDIA GeForce 8800 GT Graphics Card (VRAM 512 MB) (2560 x 1600)
    1 30-inch Cinema Display
    1 Apple NIC
    1 Apple modem
    1 Logitech 9600 Webcam
    Guest OS/Remote OS: Windows XP Professional
    Guest OS/Remote OS details: SP3, current with all Microsoft updates
    Guest OS amount of memory: Virtual Machine has 8GB, but Windows XP is only allocated 2.75GB
    Type of computer: Mac Pro
    Computer RAM: Other
    Computer RAM: 18GB (yes, eighteen)

    Any suggestions how I can get that missing 1GB allocated to Windows XP?

    Thank you,
    Don Leckie
  2. John@Parallels


  3. James Bond 007

    James Bond 007

    While I am not sure why your virtual machine has 2.75GB available for XP, you can definitely lower the memory in your virtual machine to 6GB, 5GB or even 4GB without affecting the memory available for XP. XP can address a maximum of 4GB memory anyway, and because of memory address requirements by other hardware or virtual hardware you will have at most 3.5GB of memory for XP, regardless of whether it is on a true PC or in a virtual machine.

    To assign more than 4GB of memory to your XP virtual machine is a waste of memory, unless you have other software that can take advantage of memory above 4GB (e.g. a RAM Disk).

  4. kristianmartin

    kristianmartin Bit Poster

    Im also having this problem. I understand the difference between 32-bit and 64-bit OS's, but I have seen systems show more than 2.75GB in Device Manager. I have enabled the /PAE switch in the boot.ini file, and Device Manager now shows that Physical Address Extensions are enabled, but it still only shows 2.75GB. I reduced the RAM available for the videocard to 16MB, disabled the floppy, disabled the printer, and even disabled the sound with no change. Any ideas? Is this a limitation of Parallels' code? I ask because I read somewhere that a motherboard's BIOS might have something to do with it.
  5. Tol


    Since I have the exact same amount of RAM available in my Windows XP VM, it seems to me that this is not a coincidental number.
    No matter what I do, I cannot get it to show more than 2.75GB.
  6. Olivier

    Olivier Kilo Poster

    Anyway 2.75 GB of RAM for a Windows XP machine, be it virtual or real, is just a waste. Windows XP has no way to put it at good use. 2GB is a generally accepted maximum. And shows very slim differences with a 1GB configuration.

    Windows XP 64 bits could use more RAM but won't anyway use it cleverly. So it is a waste too.
  7. Tol


    That is just not true. Collegues of mine having 4GB internal memory have notably better performance than people with 2GB mem. Specs of their laptops are exactly the same, besides the memory.
    These machines are Windows XP only, not Parallel'ed, and they show 3.5 GB usable memory.
  8. Shaddam IV

    Shaddam IV

    That's an odd statement... I know plenty of people who've got 4 Gigs in their rigs, and there are programs (e.g. Photoshop) that make plenty good use of RAM.
  9. denish


    I have the same problem


    I've got a MacBookPro with 8Gb RAM and I've allocated 4Gb to Windows XP. I need as much as I can in Windows because I'm doing development (and 2Gb is definitely not enough).

    However, XP reports only 2,883,052Kb.

    How can I get XP to see the other 1Gb or so?

  10. DPCOLE72

    DPCOLE72 Bit Poster

    Using /3GB in boot.ini has no effect. PAE was disabled in XP due to numerous driver conflicts at the time anyhow (it is available for Server 2003 as I recall...)

    Maybe settings for the VM in Parallels, to reduce the number of drivers, will free up some space. On most hardware XP installs, 3.25~3.5GB is not uncommon. Seeing less than 3GB reported by XP is rare.
  11. Specimen

    Specimen Product Expert

    Lower the amount of Video Memory, since in 32 bit the total memory address space is 4 GB, graphics memory takes a chunk out of it.
  12. DPCOLE72

    DPCOLE72 Bit Poster


    That also explains why, when running Unreal Tournament, I am limited to certain resolutions despite higher ones being available...

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