Wednesday, March 5, 2008

/3 GIG Switch and drivers *Video*

3GB switch on XP or Vista32:
The graphics vendors have re-structured their drivers to use more Operating System address space and less application address space. You may have to use the USERVA switch (i.e.. /USERVA=2800) to move the 3GB boundary down. When running up against this boundary, please limit Inventor to 1 graphics window. Do not run any other applications that are not required, as each application takes OS resources that may not be available.

  • 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 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:


  • 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.


  • 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.


  • 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.

    My test system is set up as follows:
    multi(0)disk(0)rdisk(0)partition(2)WINDOWS="Microsoft Windows XP Professional" /fastdetect
    multi(0)disk(0)rdisk(0)partition(2)WINDOWS="XP full 3GB setting" /3GB /fastdetect
    multi(0)disk(0)rdisk(0)partition(2)WINDOWS="XP 2300" /3GB /USERVA=2300 /fastdetect
    multi(0)disk(0)rdisk(0)partition(2)WINDOWS="XP 2500" /3GB /USERVA=2500 /fastdetect
    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.
  • See more at Article ID:319043

1 comment:

DarenCAvat said...

OK. That's a lot of information! Moral of the story is... "use the 3GB switch keeping in mind your video card may not support it."