Re: Umm. PDP-11s? good!
Had this discussion with some folks about why they still (!) used XP.
Apparently the reason given was that it "Just works!" (tm) and they either ignored the security issues and ran it standalone or used embedded XP which is still patched even now.
Some hospitals still run Windows 2000 because to recertify their gear with anything else would be next to impossible and besides many of the staff are in their 60's and trained for decades to use them as they are, all the others use it so diagnostic data exchange becomes a severe headache if some upgrade and some do not.
Medical imaging is one area where you are *required* to run a specific OS for the special software certification and they chose Windows 2000 a long time ago which causes no end of problems when some bean counter wonders why they spend $$$ on nearly antique hardware when some old dinosaur of a machine finally breaks down for want of an AT power supply last made in 1997.
Little tip: there's money to be made if someone can make a converter to plug a new 2015 650W PSU into, that outputs stable noise-free voltage and current for an AT motherboard.