<p>Im curious what the exact meaning of "committed" memory is when the value is queried from the MemoryUsage class.  That class explains it as "committed represents the amount of memory (in bytes) that is guaranteed to be available for use by the Java virtual machine."  Does this mean that the memory is in use by the jvm process and NOT available to other processes until it is released by the java process, or does it mean that the java process will be successful if it tries to allocate up to that amount of memory?  I realize this might be implementation specific but i am only interested in hotspot.</p>

"Does this mean that the memory is in use by the jvm process and NOT available to other processes" would be the correct one. So its less then (or equal to) the amount of memory the OS sees as taken by the JVM process.
http://java.sun.com/j2se/1.5.0/docs/guide/management/jconsole.html
(sorry no anchors to link to).