Don't forget it's clustering capabilities. I have yet to see a modern os that does it as cleanly and simply as vms.

This was key for an instalation of the largest ada codebase in the world, and the system I used to work on for a living up until a few months ago:

http://www.fas.org/spp/military/program/nssrm/initiatives/ccposr.htm

There are several papers on the internet about it, interesting stuff. If you've ever toured norad or us strategic command, or wondered what the real "WOPR" is, this is it, and it's vax/vms.

Redesigning part of it and saving taxpayers $80k in the first year from my changes (air force IDEA program) is what made my empeg purchase possible.