ZX81
Sinclair's black-and-white micro from 1981 with 1 KB of memory, which sold the home computer to people who had never pictured owning one.
The design was an exercise in deleting parts: a Z80, one custom logic chip, 1 KB of RAM and a flat membrane keyboard that was closer to a touchpad than to keys. Video went to the family TV and programs to an ordinary cassette. It was sold both as a kit and ready-built, in the US as the Timex Sinclair 1000, and shifted more than a million units.
Its limitations became folklore. The CPU drew the screen itself, so in fast mode the picture went blank whenever a program was thinking. The 16 KB RAM pack hung loosely off the back edge and could wobble out of contact an hour into typing in a listing. It still taught a generation of Britons to program, and its successor, the ZX Spectrum, added colour the following year.