One more category springs to mind--5xx would be printers (e.g. 501 and
512). Maybe I;m trying to forget about what it was like having a
machine gun on one side (501 drum printer) and a screaming banshee (512
train printer) on the other side.
8xx also includes drum storage.
I was never close to the Intercom/EI200 scene, so I talk to the RJE and
comms stuff. While I could stare at the IGS people fooling with their
big radar-screen displays, I'm not terribly familiar with the graphics
stuff either.
--Chuck