The ATARI 850 Interface Module is a necessary component for establishing communication between a console of an ATARI Personal Computer and a peripheral complying with the EAI RS-232-C standard (usually referred to as "an RS232 peripheral").

The Interface Module connects between the console and the RS232 peripheral. The Interface Module also has a parallel port, referred to as the Printer Port, Up to four RS232 peripherals may be connected to the Interface Module at one time, as well as a printer.