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Recent versions of Windows support a switch option in BOOT.INI called the /3GB switch, which adjusts the way memory is allocated between the user and the operating system. By default, the split is fifty-fifty -- up to two gigabytes for the user and two for the operating system. The /3GB switch option sets those limits at three gigs maximum for the user and one gig for the operating system.
As the name implies, /3GB was originally meant to be used in systems that have 3 GB or more of RAM -- something that is no longer quite as rare as it used to be! However, even if you don't have 3 GB or more of memory, you can still use the /3GB switch successfully if you are running memory-hungry desktop applications. Photoshop, for instance, is infamous for staking out as much RAM as it can. With /3GB enabled, there's that much more memory that the application can use.
I've written previously about using the /3GB switch in both Windows 2000 Server and Windows 2003 Server environments to bolster performance of memory-intensive services such as Exchange Server and SQL Server. But, in a desktop environment, you should consider any use of /3GB to be provisional until you determine that the application set you're using plays nicely with it. (My usual rule of thumb for seeing if something holds up under stress is to try it for two weeks under varied conditions; if it doesn't crash, it's probably okay.)
To add the /3GB switch as a separate boot option:
- In My Computer | Properties | Advanced | Startup and Recovery, click Settings.
- Click the Edit button under System Startup to edit the BOOT.INI file.
- Find the current boot entry, which typically looks like this:
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional" /fastdetect
- Copy this line and paste it at the end of the BOOT.INI file, and change it along these
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional 3GB Switch" /fastdetect /3GB
This lets you choose between a conventional boot entry and the /3GB boot entry. If something goes wrong when you use /3GB, you can always boot back into the original configuration.
- Save and close BOOT.INI.
- Click OK to close the Startup and Recovery panel.
- Click Settings again, and in the "Default operating systems:" dropdown, choose the newly
created boot entry with the /3GB switch.
- Click OK to close everything. Reboot into the new profile.
Serdar Yegulalp is editor of the Windows Power Users Newsletter. Check it out for the latest advice and musings on the world of Windows network administrators -- and please share your thoughts as well!
This was first published in July 2005