Java heap size in JMP

I'm trying to profile a simple application in java, which basically only opens an RMI interface and waits for messages. When I ope开发者_如何学JAVAn the application via TIJMP, it reports from the start:

Heap: init - 0, used - 3MB, commited - 7MB, max - 643MB.

Now I'm pretty sure that simply starting the program didn't push the memory requirement over 600MB - it's just 3 class files and listening RMI. What does the max memory really mean here? Was it ever used, or is it simply the limit of the VM and I've got only 7MB reserved (commited)?

It's probably the max heap size for the JVM, which is set with the -Xmx command line argument. The heap can increase up to that size, after which it will start throwing OutOfMemoryErrors.