PDP-10s were basically mainframes. DEC marketed them as DECSystem-10s. They were popular with universities and polytechnics, and were important in the early evolution of hacker and internet culture. DEC axed development to concentrate on VAX technology, something that caused a lot of resentment at the time. 36 bit word length I think, and 6.3 filenames crammed into 36 bits. Memory and disk space was expensive in those days.
The graphics for the movie Tron were done on a one-off prototype DEC-10 replacement.
https://en.wikipedia.org/wiki/Foonly