Atari 850 Interface module

Interface module, 1980, Atari. The 850 adds four RS-232 serial ports and one Centronics parallel port to the Atari 400/800 and their successors. It sits on the SIO bus and its own microprocessor loads a driver into the computer at boot, after which modems, serial printers and parallel printers can be used through the standard operating system calls. It was the way to connect any non-Atari peripheral in the early years of the line.