Java HotSpot Virtual Machine

Hi

I read the tuning example (from Sun web site) as following

java -Xmx3800m -Xms3800m -Xmn2g -Xss128k -XX:+UseParallelGC -XX:ParallelGCThreads=20

Comments:

* -Xmx3800m -Xms3800m
Configures a large Java heap to take advantage of the large memory system.
* -Xmn2g
Configures a large heap for the young generation (which can be collected in parallel), again taking advantage of the large memory system. It helps prevent short lived objects from being prematurely promoted to the old generation, where garbage collection is more expensive.

I can't find the definition of -Xmn, is it actually eden size? If yes, is it ok for eden size larger than halt of total heap size?

Thanks
Yanchou Han