Yes, if JBoss AS is the only thing running, and you allocate only a 4GB heap, then around 20GB of RAM will be unused. Actually, more like 18 or 19GB because the OS and various services will use some memory, the Java threads will use memory, the JVM will use memory, etc. There were some recent posts on how he JVM consumes memory. I still stand by my statements on heap sizing - a too large heap is as bad as a too small heap. There is an ideal heap size for your apps, but without monitoring the heap usage you will never know what it is. View the original post : http://www.jboss.org/index.html?module=bb&op=viewtopic&p=4235808#... Reply to the post : http://www.jboss.org/index.html?module=bb&op=posting&mode=reply&a...