3GB switch and AutoCAD® Civil 3D®

Issue

You want to know if there is a way to increase the memory usage of Civil 3D® to improve performance when working with large datasets.

Solution

By default, the Windows operating system limits the amount of physical memory available to applications to 2 GB. It reserves the remaining memory for the operating system itself. However, if you have more than 3 GB of physical memory, it is possible to increase the amount of memory available to applications, such as Civil 3D®, to 3 GB.

Autodesk has conducted some preliminary testing on this configuration and has found some improvement in performance when working with larger datasets. 

To enable the 3GB switch on Windows XP

1. Right-click My Computer. Click Properties.
2. In the System Properties dialog box, click the Advanced tab.
3. On the Advanced tab, under Startup and Recovery, click Settings.
4. In the Startup and Recovery dialog box, under System startup, click Edit.
   The Windows boot.ini file will be opened in Microsoft® Notepad. 
5. Save a backup copy of the boot.ini file on your computer, in case you need to revert back to the original version of the file.
   Note: The contents of the Boot.ini file may vary from computer to computer.
6. Select the following line in the boot.ini file:

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

7. Copy (Press CTRL+C) this line and paste (Press CTRL+V) it immediately below the original.
   Note: Your string may be different from the string shown. Be sure to copy the string from your boot.ini file, not the string shown here.
8. Modify the copied line to include “ /3GB”, as shown in the following example.
   Note: Do not overwrite any existing lines.

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

9. Save the boot.ini file and exit Notepad.
10. Click OK to close each dialog box. 
11. Restart your computer. 
12. During startup, select the 3GB option. If you do not select the 3GB option, the system will default to the 2GB memory setting.

If there are problems during startup, you may need to update some of your drivers.

To enable the 3GB switch on Windows Vista™

1. Right-click Command Prompt in the Accessories program group of the Start menu. Click Run as Administrator.
2. On the command line, enter "bcdedit /set IncreaseUserVa 3072"
3. Restart the computer.

To turn off the 3GB switch on Windows Vista

1. Right-click Command Prompt in the Accessories program group of the Start menu. Click Run as Administrator.
2. On the command line, enter "bcdedit /deletevalue IncreaseUserVa" 
3. Restart the computer.

For more information on the 3GB switch, refer to the following Microsoft MSDN article:

http://msdn2.microsoft.com/en-us/library/ms791558.aspx

If you experience any problems when using the 3GB configuration, you can switch back to the original configuration.