The first
frame buffers from Evans and Sutherland were at University
of Utah, DOD SITES and NYIT CGL as I recall. Circa 1974 to 1978.
Were those on PDP-11's, or PDP-10's? (Really early E+S gear attached to
PDP-10's; '74-'78 sounds like an interim period.)
The Picture System from 1974 was based on a PDP-11/05. It looks like
vector graphics rather than a frame buffer though.