The DEC PDP-7 is a minicomputer produced by Digital Equipment Corporation. Introduced in 1965, with a cost of only US-$ 72,000, this computer was very cheap, but quite powerful. The PDP-7 is an 18-bit architecture.
In 1969, Ken Thompson wrote the first UNIX system in assembly language on a PDP-7, then named Unics as a somewhat treacherous pun on Multics, as the operating system for Space Travel, a game which required graphics to depict the motion of the planets.
There are a few remaining PDP-7 still in operable condition, and an interesting restoration project in Oslo, Norway.