Jul 07, 2009
Nicole Morris

Autodesk Inventor 3 GB Switch

Applies to: Autodesk Inventor All Versions



Does Autodesk Inventor ® support the /3GB switch on windows XP SP1 or newer? 


  • Anyone that uses the 3GB mode, does so at their own risk.
  • Autodesk Inventor® 7 and newer supports this option.

  • Before enabling this mode, please check your workstation vendors web site for patches that may be needed for your system. HP is known to have some patches. Try searching on "3GB".

    • Tip: When Autodesk Inventor® is running, Help > About shows if the workstation is configured for this option. This is useful if you do not know in which mode the workstation was booted.

    • Tip: Before installing any driver (including a graphics driver) reboot the workstation to the standard 2GB mode, install the driver, and reboot to the standard 2GB mode so that the installation can finish.

  • This switch is available on Windows XP Professional. Attempting to use it on Windows 2000 or NT4 will cause system instability.
  • Be very careful setting up the 3GB option. If you do not leave yourself a way to boot in the standard configuration, you may have to reinstall windows.

  • MS Windows was designed to use 4GB of address space total. Of this, 2GB is reserved for the operating system and 2GB for an application. Changing this balance reduces the amount available for the operating system. When running in this mode it is important to run as few applications as possible. This includes applications that may always run at startup.

  • Go to Microsoft Knowledge base and search for "/3GB" for information on using the 3GB option on Windows XP.

  • See this Knowledge Base article for tuning information that may be needed for some graphics cards. The ability to do this tuning was introduced in SP1 for XP, then immediately patched.

  • The simplest way to enable the 3GB option is make a backup copy of the boot.ini file then, open the properties dialog of the c:/boot.ini file, remove the read only restriction, and edit it with notepad. See below for details.

  • The boot.ini is a read only file. It is also a system file. Windows Explorer must be configured to show such a file before you can see it. In Windows Explorer, Tools> Folder Options > View select the following:

    • "Hidden files and folders", click on "Show Hidden files and folders".

    • Uncheck "Hide extensions for known file types" - Useful but not required.

    • Uncheck "Hide protected operating system files (Recommended)" - OK this change.

    • Then select boot.ini, right click, select properties, uncheck read only.

    • Edit file

    • You may wish to check read only when you are finished editing the file

  • The 3GB option reduces the amount of kernel address space to 1GB. Sometimes the kernel may need more space for internal tables or other drivers. See Microsoft support for tuning information. If you have this problem, use "/USERVA=2900" (or 2800 etc.) (MB for this argument) to limit the USER Virtual Address space to less than 3GB. This allows more space for the operating system kernel if it is needed. This option is placed in the Boot.ini file just after the "/3GB" option.

  • The first time you reboot to the 3GB mode immediately go the the My Computer properties > Advanced tab > Settings > Advanced tab > and change the maximum amount of virtual memory to 4 GB. This is part of the microsoft requirements.

  • Graphics vendor specific information is available for these vendors:

    • 3Dlabs:

      The Wildcat III/4 cards do support the 3GB option.

      The Wildcat VP880 & VP990 use 256MB of kernel memory. The 3GB option reduces the amount of kernel address space to 1GB. If other devices are using large amounts of kernel memory, then this may cause a Wildcat VP driver to fail to load (see Microsoft support for tuning information). If you have problems, use set /USERVA=2900 (or 2800 etc.) to reserve an additional 100MB (or more if needed) for the kernel with these cards.

    • ATI: The recommended mode of operation assumes that you have a 4GB system, a reasonable card (256MB or better) and setting the flag /userva=2500. See for information on tuning your system so that stability is maintained.

    • Matrox:

    • Nvidia: The 3GB option appears to be supported by drivers newer than 4072. Using the latest drivers, no problems have been found with Nvidia cards. Not all cards were tested.

    • NEC: Not tested

  • My test system is set up as follows:

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

  2. multi(0)disk(0)rdisk(0)partition(2)WINDOWS="XP full 3GB setting" /3GB /fastdetect

  3. multi(0)disk(0)rdisk(0)partition(2)WINDOWS="XP 2300" /3GB /USERVA=2300 /fastdetect

  4. multi(0)disk(0)rdisk(0)partition(2)WINDOWS="XP 2500" /3GB /USERVA=2500 /fastdetect

  5. multi(0)disk(0)rdisk(0)partition(2)WINDOWS="XP 2800" /3GB /USERVA=2800 /fastdetect


Always copy and edit the last line of your Boot.ini file. It may be different from my last line. Using my line may make your system unable to boot.


  • Line 1 is the original last line in my boot.ini file. As the first line in this group, it will be the default line if one does not make a different selection during the boot process. This is my escape hatch.

  • Line 2 is modified to boot in the 3GB mode which allows 3GB of address space to the application and 1GB to the windows kernel.

  • Line 3 provides 2.3GB of address space to the application and 1.7GB to the Windows kernel.

  • I have all of these combinations available to test different hardware and drivers. You should not need to have all of these lines in your boot.ini file.

  • Use what works. You have to allow enough space for the Windows kernel to run.

  • Once you are finished modifying the boot.ini file, please protect it by changing it to read only.

  • Microsoft has identified a problem for systems with multiple SCSI controllers.


For printable pdf version click here.