Enabling the 3 GB Feature on 32-Bit Machines

Revit is a 32-bit application, which is limited to 4 GB of virtual address space. Typically, on a 32-bit machine, Microsoft® Windows® reserves 2 GB of the 4 GB virtual address space of any process for the operating system and leaves the remaining 2 GB for the application process (including the space for the code pages, the stack, and all dynamically allocated memory). The 3 GB feature divides the virtual address space differently on 32-bit machines, providing 3 GB for the application and 1 GB for the operating system.

On 64-bit machines, the 3 GB switch does not apply because Windows does not reserve virtual address space for the operating system, allowing Revit to use up to the available 4 GB.

Before enabling the 3 GB feature, see 3 GB Feature Considerations.

To enable the 3 GB feature on Windows XP

1. Open the boot.ini file.

   This file is typically located in C:\, and it is a protected operating system file. To see it, in a Windows Explorer window, click Tools menuFolder Options. On the View tab, clear Hide protected operating system files, and click OK.

2. In the operating systems section, copy the original line containing the boot path, then modify the copied line to add the option (/3GB) and the display string that identifies the boot option.

   Examples of the line to copy and the modified version of the line are shown below. The modified portions of the copied line are in bold.

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

   When you start your computer with the modified boot.ini file, you see the following options to select from:

   • Microsoft Windows XP Professional
   • Microsoft Windows XP Professional 3GB

To enable the 3 GB feature on Windows Vista

1. Click Start menuAll ProgramsAccessories, and run the command prompt.
2. Enter BCDEDIT /SetIncreaseUserVa 3072, and exit the command prompt.
   NoteIf you are not able to set this value, when you run the command prompt, right-click, and click Run as Administrator.
3. Reboot the computer.

   The switch is now set. It is not necessary to make a selection when you reboot the computer; it is automatically enabled.