Editing Physical Address Extension settings

To cosmetically correct the issue where Windows XP only shows 3.5GB of memory or less when 4GB of physical memory installed, follow the step by step guide below:

  1. Click 'Start' then 'Control Panel'.
  2. Once the control panel has opened, double click 'System' or 'Performance and Maintenance' then 'System'.
  3. In the System Properties window, click the Advanced tab.
  4. Toward the bottom of the Advanced window, look for the Startup and Recovery section.
  5. Click the Settings button.
  6. The Startup and Recovery window opens to the System Startup section.
  7. Click the Edit button to open the Boot.Ini file in Notepad.
  8. Place the cursor after /fastdetect, and then press the spacebar.
  9. Type /PAE. (PAE is short for Physical Address Extension.)

    The Boot.ini file should resemble this:

    [boot loader]
    timeout=30
    default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS
    [operating systems]
    multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional" /fastdetect /PAE

  10. In the File menu, click Save.
  11. Exit Notepad, Start Up and Recovery and System Properties.
  12. Restart your machine. WindowsXP should now recognize REPORT 4GB of memory.

If Windows does not detect the full amount of memory after C, please follow the trouble shooting steps below:

  • Check if the full amount of memory is registered in the BIOS.
  • If the full amount of memory is registered by the BIOS, the problem lies with the operating system. Please contact Microsoft for further assistance. You may have to upgrade to a 64-bit operating system and processor to enable the full 4GB of memory.
  • If the full amount of memory is not detected by the BIOS, please try each module individually in the system. For example, if you have 4 x 1GB modules, try them in pairs. If both pairs of modules register 2GB in the BIOS and within windows, it shows the memory is working correctly. Try installing all 4GB of memory again and check the BIOS. If the BIOS still does not register the full amount, the problem lies with the motherboard. Please contact the system/motherboard manufacturer for further assistance.
  • Some systems/motherboards reserve a certain amount of memory for system usage, i.e. PCI slots and therefore the actual displayed memory amount is less than the physical installed amount. Please consult your system/motherboard manual for further information.