A little bit of both, but some of this stuff is probably still running on minicomputers. Think DEC PDP-11 and HP2100 series stuff.
System E for the WIN! 50 years old is rockin'. We still have 8 inch disks working the US Nuclear Deterrent but do we really want any air traffic control system running on Windows? IBM is going to have to come in with iSeries and Z13 mainframes and rebuild all that shit and it's gonna cost a lot.
If you dig into the windows agreement, there are things that MS prohibits running on it. I can't remember if ATC is there, it's been decades since I had to worry about it.
I sold all of my 8" stuff for a hefty premium some years ago. I'm selling my remaining 5 1/4 stock now...amazing how many people think this stuff is free.