Using more than 2.5Gb RAM with 4Gb installed

Hey all,

Recently I built a new computer and installed 4Gb of DD2RAM. I have Windows XP SP3 32bit installed and notice that only 2.50 Gb is recognised as total physical memory under the performance tab.

Now Ive read through the countless other posts and know the issue with 32 bit operating systems and their inability to recognise all the 4Gb of RAM (due to onboard hardware devices sharing the address space).

However I find it quite odd that ONLY 2.50Gb is being used. I have a 512Mb Geforce 9600GT graphics card and the only other hardware devices are my sound card (Sound Blaster Audigy 2 ZS) and a wireless Gigabyte Wp01GS network adapter.

I am not ready to move to Vista/Windows 64bit because I know my sound card is not fully compaitble with it.
I would really appreciate it if an expert here knows more about CPU architecture/memory mapping and can offer some kind of suggestion in getting windows to use at least 3- 3.5Gb (which I think should be possible).

My other specs are:
CPU: E8400 Core2 Duo @ 3Ghz (at the moment)
RAM: PC8500 DDR2 Kingston RAM (1066Mhz) -->(bought for overclocking purposes)
Gigabyte EP45-UD3R Mobo
Galaxy 512Mb Geforce 9600GT

Thanks for all the help guys
13 answers Last reply
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  1. Everything you're seeing is completely normal with a 32bit OS. The 32bit OS is really only capable of addressing about 3GB of RAM. Since your video card is 512MB, the rest of your system can only be addressed 2.5GB. :)

    2.5GB + 0.5GB = 3GB.

    Your work around is to purchase and install the 64bit Windows XP or 64bit Vista.

    I used to use an Audigy 2 sound card I think. And I'm pretty sure I had found drivers for it that worked with Windows XP 64bit.

    Edit: I checked out the website for you. Here's a link to the Vista 64bit driver for your sound card.

    Vista Driver for Audigy 2 ZS

    Vista 64 / Vista 32 Audigy 2 ZS Driver
    Release date : 16 Mar 07
    File Name : SBAXVSD_PCDRV_LB_2_12_0002.exe
  2. jerreece, thanks for your reply.

    If that is the case, then why are some setups easily able to use 3.5Gb (sometimes even more).

    It doesnt make sense that a whole 1Gb of RAM is being lost somewhere, as the only other device that should be sharing the address space is the Graphics card ---> (4Gb - 0.5Gb = 3.5Gb).

    I have read posts about changing BIOS setting or something to do with memory mapping (or PAE) but dont full understand it. Can anyone enlighten me on a possible fix besides upgrading to 64 bit?

  3. Some boards (Gigabyte for instance) tend to reserve a lot more MMIO address space below the 4G-mark than needed. And address space reserved for MMIO cannot be used for RAM.

    32bit XP can address 4GB total.
  4. Do you have service pack 1 installed for Vista? That should make it so that all 4GB shows up. Blah blah about how much can be addressed, I am only talking about how much is shown.
  5. Well I think it has as much to do with the 32bit OS as it does hardware. I'm honestly not your best bet for trying to squeeze out that extra 512MB of RAM. Basically though, your system is currently using 3GB total (granted only 2.5GB of that is your system RAM).

    If you go to the Tomshardware front page, you'll find a recent article from Chris Angelini discussing this whole 64bit issue in regards to gaming. The whole shift from 32bit to 64bit really has more to do with the ability to use larger amounts of memory. The old 32bit system simply wasn't capable.
  6. jerreece,

    Known Issues
    Applications from the original Sound Blaster Audigy CD will not work with this download.
    Users are advised to use Audio Console included in this download to change speaker configurations.
    This driver does not support the following:
    Decoding of Dolby® Digital and DTS™ signals
    DirectSound®-based EAX games
    6.1 speaker mode.
    SPDIF passthrough is supported on Vista 32-bit only. "

    I would hardly call that support ;P

    If the problem is a physical limitation of my particular mobo, then I am very dissapointed :(. 1Gb is alot of ram...
  7. It is probably not a physical limitation of your board, but rather that the BIOS hasn't been programmed to make optimal use of the lower 4GB address space. So when using an OS that has a limitation of 4GB, you'll lose a few extra bytes.
  8. Ok, so this is unrelated, but if I were to upgrade should I get vista 64bit or XP64bit? Also I know in the past Vista was alot slower than XP (before the hotfixes) How does Vista SP1 64bit compare to windows Xp 32bit in terms of general performance? Has there been any website to make this direct comparison?

  9. jerreece said:
    The 32bit OS is really only capable of addressing about 3GB of RAM. Since your video card is 512MB, the rest of your system can only be addressed 2.5GB. :)

    2.5GB + 0.5GB = 3GB.

    A 32 bit OS is capable of addressing 4GB.
  10. Just to update, I disabled the onboard LAN on the motherboard (I dont need ethernet as I have wireless) and now windows is reporting 3Gb, which I can live with :).
  11. Check to see if there is an option in your BIOS called Memory Mapping, or Memory Remapping. If your BIOS is detailed it will even have Software Remapping, and Hardware Remapping. You want to enable software remapping. Some BIOS's do not by default provide for memory addressing space beyond the first 3 gig of installed memory. Enabling the remapping feature will allow the system access to memory beyond 3 gig.
    The easiest way to tell if you need to do this is watch the memory count at POST.
    If it counts all 4 gig, you are nothing.
    It it only counts up to 3 gig, you need to enable memory remapping.

    Then you can be assured that your OS has access to all the memory it can use.
  12. jitpublisher, did you read what I wrote to you about memory remapping the other day?
  13. With GIGABYTE GA-EP45-UD3L, 4GB RAM kit, and XFX PVT95GYDQ3 9500GT 512Mb video card I get 2.5GB RAM with 32-bit Windows XP. If I disable the motherboard onboard ethernet controller from the bios, windows now sees 3.0GB. .....MMIO as stated above.
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