i875p Canterwood does not see 4GB RAM - Sees 3GB RAM

Discussion in 'Asus' started by Julius Moreland, Apr 8, 2004.

  1. This is very frustrating and I'm feeling a little cheated here...
    Please anyone give me a real answer.

    I've built a Photoshop workstation based on the P4C800-E Deluxe. I
    have 4GB of Dual-Channel PC3200 by Micron/Infineon.

    When I put in one stick the MB shows ~1GB, 2 sticks ~2GB, 3 sticks
    ~3GB, but 4 sticks is ~3GB not ~4GB. Asus says this is "normal" and
    happens on other chipsets by Via and SiS, but I just can't take that
    for a real answer.

    I've swapped the sticks around to no avail. Doesn't matter if I have
    2 sticks in Dual or Single-Channel mode, they still POST at ~2GB so I
    can't blame it on the Dual-Channel Mode.

    I know there's *some* overhead for AGP aperture and MCH 1.4, etc. but
    that does not account for the failure to utilize over 1GB of fine RAM!

    I've read the MCH whitepapers in Intel's site, but they don't account
    for this much loss.

    I'm on the latest BIOS, have tried APIC and no APIC, MCH 1.1 and 1.4.

    Arrrgghhhh! What is going on? Intel is no help, and ASUS claims a
    note from their "engineers" explains it all, "this is normal," but
    also says some people have reported utilizing 3.8GB. How?

    Anyone know the real story?
    Julius Moreland, Apr 8, 2004
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  2. Julius Moreland

    Paul Guest

    I bet if you remove your AGP video card and use a PCI video card,
    more of the memory will be available. The tough part will be getting
    Windows to recognize the extra memory you are working so hard to
    free up. (I wish I knew of a software utility that can display
    the memory map for a system - the info you need to debug the problem
    would be found in the Northbridge control registers, but I don't know
    how to get at that info.)

    Daytripper gave me this reference before:

    This article references a /3GB flag for booting:

    Paul, Apr 9, 2004
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  3. There is a lot more 'overhead', than just the AGP aperture. Basically every
    PCI card and controller will be using some addresses at the top of the
    memory. Looking at device manager, and the 'memory range' for cards, will
    give an idea of just how much is involved. For instance, on the 'AGP' video
    card, it is typical to see perhaps three seperate memory ranges in use. One
    is down 'low', and corresponds to the normal EGA/VGA addresses in the base
    memory, and then a couple in high memory as well. On a modern card, expect
    perhaps about 140MB in total for the video card alone!. Then add other
    devices (RAID controllers have a BIOS, network cards, a window into memory,
    etc. etc..). Typically, you will be lucky to get away with less than 0.5GB
    to 0.7GB being used by the cards. It is common to be able to use more RAM
    area, on motherboards designed for 'server' applications. Using a PC video
    card, and some more careful mapping of the addresses given to devices (and
    not having things like built in sound, which again use memory areas), brings
    the useage down significantly, also many of these when switched to fully
    32bit mode, disable the low memory addresses, and gain back the area here.
    Be aware, that the normal releases of Windows, themselves place limits on
    the RAM available to programs, so the gain beyond about 3.2GB, is little,
    unless you are using a custom modified OS. The amounts useable on boards
    have declined over the last few years, with increasing numbers of devices
    mapped into the upper memory 'as standard'. So the presence of multiple
    PCI-PCI bridges, USB controllers, sound cards etc. etc., have all eroded the
    maximum useable RAM...
    Now your problem goes a little 'beyond' this. I'd have certainly expected
    you to see perhaps 3.3, to 3.5GB available. It may be as simple as a limit
    in the BIOS's ability to 'report' memory. If you run a memory diagnostic
    tool like Memtest86, what does it report?.

    Best Wishes
    Roger Hamlett, Apr 9, 2004
  4. Julius Moreland

    Anon Guest

    How much memory does the BIOS System Information show? Have you tried
    running Memtest86+, if so how much memory does is show? How much Total
    Physical Memory does Windows Task Manager show?
    Anon, Apr 10, 2004
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