/3GB option in boot.ini file in Windows XP allows to give any application up to 3 GB of RAM. However, there is no such option in Windows Vista or Windows 7, the boot.ini file was replaced with a utility called BCDEdit
In order to set it up, just run this command:
bcdedit /set IncreaseUserVa 3072
and restart the computer.
This command removes the option
bcdedit /deletevalue IncreaseUserVa