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. You should also verify that you have sufficient virtual memory allocated for your purposes before enabling the 3GB switch.

 To verify virtual memory allocation on Windows XP

1. Click Start menuSettingsControl Panel.
2. In the Control Panel, double-click System.
3. In the System Properties dialog, click the Advanced tab.
4. In the Performance field, click Settings.
5. In the Performance Options dialog, click the Advanced tab.
6. In the Virtual Memory field, change the Initial and Max values to twice your physical memory.

   Physical Memory	Recommended Paging File
   2 GB	4096 MB
   3 GB	6144 MB
   4 GB	8192 MB

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.

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

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

See our product support page for more information.