This article describes how to use the 4GT RAM Tuning feature in Microsoft Windows 2000 Advanced Server and in Microsoft Windows 2000 Datacenter Server.
In Windows 2000, the per-process address limit is 2 gigabytes (GB). You can expand this limit to 3 GB by taking advantage of the 4-GB memory tuning feature in Windows 2000 Advanced Server and in Windows 2000 Datacenter Server. This feature is named 4GT.
4GT reduces the potential random access memory (RAM) that is allocated to the Microsoft Windows NT kernel from 2 GB to 1 GB. This increases the user mode address space to 3 GB. Before you can take advantage of 4GT in Windows 2000 Advanced Server or in Windows 2000 Datacenter Server, you must modify the Boot.ini file to enable application memory tuning. To do this, add the /3GB parameter to the ARC path in the Boot.ini file, as follows:
Note This sample ARC path assumes that you are running Windows 2000 Advanced Server.
No new application programming interfaces (APIs) are required for application memory tuning support. However, Microsoft recommends that you do not provide every program with a 3-GB address space.
You can use the Imagecfg.exe file to provide selective use of application memory tuning in Microsoft Windows 2000. Executable files that can access the 3-GB address space must have the IMAGE_FILE_LARGE_ADDRESS_AWARE bit set in their image headers. You can set this bit by using the Imagecfg.exe utility; this utility is included on the Windows 2000 Server Supplement One Resource Kit CD-ROM. For example, to modify an executable file that is named Test.exe, use the following command syntax:
Imagecfg -l test.exe
Note Some manufacturers link their programs to use application memory tuning, and if this is the case, you do not have to use the Imagecfg.exe file. The linker also has a switch (/ LARGEADDRESSAWARE) to link executableswith the IMAGE_FILE_LARGE_ADDRESS_AWARE bit. If you set this bit and then run the program on a system that does not have 4GT support, the program will not be affected. For more information, see your program documentation.
The Imagecfg.exe file is available in the Windows 2000 Server Supplement One Resource Kit. If this resource kit is installed on your system, you can find Imagecfg.exe in the C:\Program Files\Resource Kit" default location folder. If the resource kit has not been installed, you can extract Imagecfg.exe from the Debug.cab file on the root of the Windows 2000 Server Supplement One Resource Kit CD-ROM.
For additional information about 4GT, click the following article number to view the article in the Microsoft Knowledge Base:
171793 Information on application use of 4GT RAM Tuning