There have been many discussions on the internet about the maximum available memory Java programs can use. I'd like to use more than 4 gigabyte of memory in ImageJ, is that possible?

Yes, you can if you use a linux AMD64 and sun java runtime environment. I used ubuntu (http://www.ubuntu.com) version 7.04 AMD64 and tested on an AMD athlon and an AMD dual opteron system. Although the sun website says that the only system able to use more memory is solaris I found no problems increasing the memory size up to 8 GB using the following statement:

java -jar -XmxNg -XX:+AggressiveHeap ij.jar

Where N is replaced for the number of gigabytes you like to use.

Note: Using more memory than the amount of ram you have makes the system very slow, and make sure that you use the right java binary, or point directly to the sun java binary, for ubuntu that is:

/usr/lib/jvm/java-6-sun/jre/bin/java

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