1. This forum section is a read-only archive which contains old newsgroup posts. If you wish to post a query, please do so in one of our main forum sections (here). This way you will get a faster, better response from the members on Motherboard Point.

32bit OS cannot see 4GB of RAM on modern chipset

Discussion in 'PC Hardware' started by J de Boyne Pollard, Nov 5, 2007.

  1. MSS> I have a machine built on Intel G33 chipset (Asus P5K-V mobo).
    MSS> 64bit OS (2003 R2 SP2 Ent) sees all 4GB of really present
    RAM.
    MSS> 32bit OS (XP SP2 Pro) sees only 3.24GB of RAM, with PAE on.
    MSS> Why is this?

    Read <URL:http://dansdata.com./askdan00015.htm>.

    MSS> Any chances of fixing this by tuning some OS registry
    MSS> settings or the BIOS settings?

    No.
     
    J de Boyne Pollard, Nov 5, 2007
    #1
    1. Advertisements

  2. Read <URL:http://dansdata.com./askdan00015.htm>.

    Can Microsoft people confirm or deny this cite from the above URL:

    "For this reason, Microsoft changed the behaviour of the /PAE option in all
    versions of WinXP as of Service Pack 2. They fixed the endless driver problems
    by, essentially, making /PAE in XP not do anything. All versions of WinXP
    except for the x64 Edition now have a hard 4Gb addressing limit, no matter what
    hardware you use them on and what configuration you choose."

    Is this true? Well, PAE is definitely on, since Data Execution Protection
    requires PAE (no NX bit in pre-PAE PTEs), and is on even on 1GB Acer laptop.

    But what about the memory addresses? are they really truncated by the OS to
    32bit even in PAE mode? what about Server 2003 32bit? is it suffering from the
    same artificial limitation?

    If it is so - is there any Windows setting to switch this off and use 36bit PAE
    physical addresses? I expect only the miswritten and buggy drivers have PAE
    issues, and, since I have no PCI cards in the machine, I expect the out-of-the
    box MS's drivers to be fine with 36bit physical addresses.
     
    Maxim S. Shatskih, Nov 5, 2007
    #2
    1. Advertisements

  3. -|MSS> I have a machine built on Intel G33 chipset (Asus P5K-V mobo).
    -|MSS> 64bit OS (2003 R2 SP2 Ent) sees all 4GB of really present
    -|RAM.
    -|MSS> 32bit OS (XP SP2 Pro) sees only 3.24GB of RAM, with PAE on.
    -|MSS> Why is this?
    -|
    -|Read <URL:http://dansdata.com./askdan00015.htm>.
    -|
    -|MSS> Any chances of fixing this by tuning some OS registry
    -|MSS> settings or the BIOS settings?
    -|
    -|No.
    I'm running an Intel Pentium 4, and XP Home Edition with all available Windows Updates.
    This is a Dell Optiplex GX620 with 4 GB RAM. The system Icon shows that a little less
    than a half GB is used for various caches (like ATI adapters). The Task Manager shows:
    Total Physical Mememory = 3668036 K or 3.66 GB.
    Commit Charge = 374M/5469M.

    So what do you mean by "see"?

    Skip
     
    Herman D. Knoble, Nov 5, 2007
    #3
  4. Total Physical Mememory = 3668036 K or 3.66 GB.
    Total Physical Memory is _significantly_ smaller then 4GB.
     
    Maxim S. Shatskih, Nov 5, 2007
    #4
  5. True. On 32-bit client versions of the OS you're limited to physical
    addresses < 4GB even with /PAE turned on. /PAE still gets you NX
    compatibility but won't let you see those last few MB. It's a policy
    decision that included some marketing decisions as well as the expectation
    that too many existing PCI drivers were going to fall over when faced with a
    36-bit address.

    -p
     
    Peter Wieland [MSFT], Nov 6, 2007
    #5
  6. True. On 32-bit client versions of the OS you're limited to physical
    Thanks Peter!

    Am I correct that 32bit Server 2003 is free from this limitation?
     
    Maxim S. Shatskih, Nov 6, 2007
    #6
  7. Yes it should be.
     
    Peter Wieland [MSFT], Nov 7, 2007
    #7
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.