title: Java application memory size
body: <p>While either IntelliJ or Eclipse are running, I can see how much heap they are using from inside the application from the progress bar at the bottom.. it always indicates a sub 512 MB value which the max size allocated on startup.
  Now in many cases, if I look from the OS (Linux) it says that the app is using about 1300 MB, I understand that the libraries, stack, memory mapped files, ... are not in the heap... 
  But why is the difference that big? There is usually about 1GB difference...Why?</p>
  
  <p>Thank you.</p>