Q:

What is the difference between MaxPermSize and MaxPermGen in Jboss configuration?

There are two attributes that I figured out. I guess some of the Jboss versions support MaxPermGen and some other versions support MaxPermSize.
Thats my guess only. What is the exact difference between those two attributes ?
I tried to replace MaxPermGen with MaxPermSize in my Jboss 5.1.0 to findout the difference. JBoss failed to start.

A:

I'm not aware of any MaxPermGen option of the Sun VM (in any version of the JVM) and invalid options will prevent the JVM to start properly. 
However, MaxPermSize is correct and allows to define the Size of the Permanent Generation.
Reference

A Collection of JVM Options (most exhaustive resource I know)

