A few years back I did some consulting for one of the big cargo train companies. They had a big mission control type room with maps of all the tracks they manage, with lights indicating switch status and train positions and so forth. The actual switches were managed by a bunch of racks full of PDP-11s running RSX-11, equipped with digital I/O boards linked to the switch motors and sensor relays out in the field. The computer room was amazing, immaculately clean and completely free of static, with air cleaners that popped periodically when they caught a piece of dust. I asked them why they still used those, seeing as there are much more modern computers capable of doing the exact same job, and they replied that they just didn't have faith that new machines would be as reliable.