Issue with new DDR2 RAM


I've just recently made a few upgrades to my home computer. I've upgraded the CPU and replaced 2GB of RAM with 4GB.

My previous layout had two sticks of 1gig and I've upgraded to two sticks of Kingston 2GB (link -

My issue is only CPU-Z is registering the 4GB. On both DxDiag and AIDA32 its telling me I only have 2558MB RAM.

I find this strange; any suggestions as to why this would be happening?
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  1. Best answer
    any suggestions as to why this would be happening?

    No mention of which operating system is used. Install a 64 bit operating system.


    This behavior is the expected result of certain hardware and software factors.

    Various devices in a typical computer require memory-mapped access. This is known as memory-mapped I/O (MMIO). For the MMIO space to be available to 32-bit operating systems, the MMIO space must reside within the first 4 GB of address space.

    For example, if you have a video card that has 256 MB of onboard memory, that memory must be mapped within the first 4 GB of address space. If 4 GB of system memory is already installed, part of that address space must be reserved by the graphics memory mapping. Graphics memory mapping overwrites a part of the system memory. These conditions reduce the total amount of system memory that is available to the operating system.

    The reduction in available system memory depends on the devices that are installed in the computer. However, to avoid potential driver compatibility issues, the 32-bit versions of Windows Vista limit the total available memory to 3.12 GB. See the "More information" section for information about potential driver compatibility issues.
    If a computer has many installed devices, the available memory may be reduced to 3 GB or less. However, the maximum memory available in 32-bit versions of Windows Vista is typically 3.12 GB.


    An x64 (64-bit) version of Windows must be used.
  2. Ah cheers. I'm running 32-bit Windows XP Home Edition so that makes sense.

    Thank you for a very comprehensive answer!
  3. Best answer selected by lucio vichente.
  4. You're welcome. Maybe Windows 7 64 with Superfetch is in your future.
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