How to enable the 3GB switch in Windows

Nov 1, 2014


You want to make more memory available to your Autodesk application by enabling the 3GB switch on your 32-bit version of Windows XP, Windows Vista, Windows 7, or Windows 8 operating systems.

While the 3GB switch may be a useful tool that allows you to access more memory for your Autodesk application, it should be mentioned that not all Windows updates or hardware and graphics drivers work well, or at all, with the 3GB switch enabled. In fact, some limitations may even apply to certain features that ship with your Autodesk application. If you experience any unexpected or abnormal behavior with the 3GB switch enabled, we recommend that you disable it and move to a 64 bit application.

Note: Inventor users should reference the help topic Increase performance and capacity regarding the limitations of the 3GB switch.


Windows Vista, Windows 7, or Windows 8

To enable the 3GB switch:

  1. Right-click on the Command Prompt icon in the Accessories program group of the Start menu. Click Run as Administrator.
  2. At the command prompt, enter: bcdedit /set IncreaseUserVa 3072
  3. Restart the computer.

To disable the 3GB switch:

  1. Right-click on the Command Prompt icon in the Accessories program group of the Start menu. Click Run as Administrator.
  2. At the command prompt, enter: bcdedit /deletevalue IncreaseUserVa
  3. Restart the computer.

Windows XP

To enable the 3GB switch:

  1. Right-click My Computer. Click Properties.
  2. In the System Properties dialog box, click the Advanced tab.
  3. On the Advanced tab, under Startup and Recovery, click Settings.
  4. In the Startup and Recovery dialog box, under System startup, click Edit. The Windows boot.ini file will be opened in Microsoft® Notepad.
  5. Create a backup copy of the boot.ini file. Note: Boot.ini files may vary from computer to computer.
  6. Select the following line in the boot.ini file:

    multi(0)disk(0)rdisk(0)partition(2)\WINDOWS="Microsoft Windows XP Professional" /fastdetect

    Press Ctrl+C to copy the line and then press Ctrl+V to paste it immediately below the original line.

    Note: Your text string may be different from the text string in this solution, so be sure to copy the text string from your boot.ini file, and not the text string included here.
  7. Modify the copied line to include “ /3GB”, as shown in the following example:

    multi(0)disk(0)rdisk(0)partition(2)\WINDOWS="Microsoft Windows XP Professional 3GB" /3GB /fastdetect

    Note: Do not overwrite any existing lines.
  8. Save and close the boot.ini file.
  9. Click OK to close each dialog box.
  10. Restart your computer.
  11. During startup, select the 3GB option. If you do not select the 3GB option, the system will default to the 2GB total memory setting.

    Note: If problems occur during startup, you may try to resolve the issue by updating some of your drivers.  However, recall the notice at the beginning of this solutions that note all Windows update or hardware and graphics drivers work with the 3GB switch enabled.

For more information on the 3GB switch, refer to the following Microsoft MSDN article: /3GB.


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