Here is the pdp-11, birthplace of Unix: https://en.m.wikipedia.org/wiki/PDP-11
It's by all means a mainframe. Same goes for the vax which followed it.
"Mid range" and "Mini computers" came up in the 1980s/1990s, e.g. as Department file and print servers.
> The PDP-11 is a series of 16-bit minicomputers
It’s a class of computers in the 1960’s that was distinct from mainframes because they were so much smaller and cheaper, even though today all 60’s computers feel equally huge.
The PDP-11 was a minicomputer. It did not have the data throughput to compete with a mainframe.
Minicomputer = wardrobe/fridge size computers
Microcomputer = your idea of minicomputer