IBM User Guide for Java V7 on Windows > Troubleshooting and support > Problem determination > Windows problem determination > Setting up and checking your Windows environment

Windows 32-bit large address aware support

The 32-bit IBM JVM for Windows includes support for the /LARGEADDRESSAWARE switch, also known as the /3GB switch. This switch increases the amount of space available to a process, from 2 GB to 3 GB. The switch is a Windows boot parameter, not a command line-option to the JVM.

This switch is useful in the following situations:

• Your application requires a very large number of threads.
• Your application requires a large amount of native memory.
• Your application has a very large codebase, causing large amounts of JIT compiled code.

To enable large address support, modify your boot.ini file and reboot your computer. See the related links for more detailed information.

After enabling the /3GB switch, the JVM gains 1 GB of extra memory space. This extra space does not increase the theoretical maximum size of the Java™ heap, but does allow the Java heap to grow closer to its theoretical maximum size (2 GB - 1 bytes), because the extra memory can be used for the native heap.

Related links

• How to Set the /3GB Startup Switch in Windows: http://technet.microsoft.com/en-us/library/bb124810.aspx.
• Memory Support and Windows Operating Systems: http://www.microsoft.com/whdc/system/platform/server/PAE/PAEmem.mspx.
• A description of the 4 GB RAM Tuning feature and the Physical Address Extension switch: http://support.microsoft.com/kb/291988/.

Parent: Setting up and checking your Windows environment

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