If I understand you correctly, you are using the -d64 option, and the reason you are using this option is because of a library, named Timesten, that you are using in your application. So let me ask you this. If you run without -d64 and without Timesten, does JBossAS show reasonable memory usage? (I realize that to do this you will not be able to deploy your application.) If the answer to that question is "yes," then why are you asking this question in the JBoss forums and not directing this question to the Timesten developers, or to Sun (it's their JVM that implements the -d64 option). Also, the -Xss governs the stack size for each thread. Thus you are using 157*8K or memory just for the stacks. Your heap setting is 1GB. The JVM will use at most that much memory for Java objects. The rest of the memory is used by the JVM. Wait a minute, that is not correct. The Timesten library is a shared object, correct? Well, it also uses memory. Try this: run JBossAS without your app (and thus without Timesten) but keep the -d64 option on the command line. Look at the memory usage. Compare that to the 5.5GB you mentioned. The difference is what is being used by Timesten. If that is excessive, talk to the developers of Timesten. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4166201#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...