During my browsing, I've run across mention of the Emerson "Tape Pac"
2000 series, a half-inch cartridge tape system targeted at
minicomputers, and it seems, the PDP-11.
Here's a mention in IEEE Computer, about the new products at the 1976 NCC:
https://www.computer.org/csdl/mags/co/1976/06/01647391.pdf
(That was about the same time as "The Milpitas Monster")
I can't find of photos of the thing. Has anyone run into one of these?
--Chuck