Not sure how to draw the line. I am doing some study on the GC. Some GC tuning requires the knowledge of the CPU core, so will it be a hardware or Java question?
Sorry I did not state the OS here earlier. I am using Linux with Java 6. If the OS will swap the memory even I allocate a fixed number of memory to the heap, it will be affected my decision on fine tuning the GC. I think it is a Java question.