The Atari 850 Interface is an external box that adds 4 DB-9 serial ports, a parallel port, and an I/O port pass-thru to the Atari 8bit computer line. The DB-9 serial ports use a nonstandard pinout since they predate the IBM AT and it uses the same power supply unit as the Atari 800 computer and 810 disk drive. The 850 plugs into the same I/O bus as the Atari modems and disk drives.

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