From the release notes of the J2EE reference implementation version 1.3 beta 2:
"Scalability and Memory Requirements
We have experienced intermittent problems when the J2EE server is run on a system with less than 128 MB of memory, or when a large number (> 16) of J2EE applications are deployed, or when a large number (in the thousands) of enterprise beans are instantiated. If you run out of memory, shutdown and restart the J2EE server."
Jesper