Connecting Peripherals to Atari 8-bit Computers

Computers today generally have just one primary type of input/output port: USB-C or Thunderbolt, both of which use the USB-C connector. My MacBook Air has two USB-C ports for peripherals, plus a MagSafe connector for charging and a 3.5mm port for an audio device. Other computers might have the older USB-A port and perhaps an HDMI port, but the days of a wide variety of ports on computers are long gone.

It can certainly get confusing as to what type a USB-C port is since you cannot often tell just by the connector, but this is certainly much, much better than things were in the old days.

Early computers usually had multiple ports, usually different ports for different things. There could be a port for a cassette interface, one for the floppy drive, one for the printer, controller ports, etc.

For most of its IO, the Atari 400/800 used its proprietary SIO (Serial Input/Output) port for connecting peripherals. Although there was only a single SIO port, devices usually have an extra port on them so that they could be daisy-chained.

In many ways, this SIO port was the precursor to USB, but I’ve already written about that.

As cool as the SIO port was, if you wanted to connect other peripherals that didn’t use SIO to your Atari, such as a printer or modem, you were out of luck.

Although Atari sold their own printers, they were usually not all that great. If you wanted to use an industry-standard Epson dot-matrix printer, for example, you could not do so directly since the parallel connector used by printers at the time could not be directly connected to the Atari.

The same was true of modems, which used the RS-232 serial interface.

Atari 850 Interface Module

The solution to this was to use an interface box. Atari thought of this, of course, and alongside the 400/800 release Atari also released the Atari 850 interface module. This box had industry-standard parallel and RS-232 ports on it and it connected to your Atari via SIO.

At $200 ($918 in 2026), this interface box was not cheap, adding to the expense of using industry-standard peripherals. It’s price did drop over the years, but when then XL line was introduced, there was no equivalent to the Atari 850 interface. So by 1984 this device became somewhat tricky to find.

This was mostly a problem for people that wanted a modem. Atari didn’t have good SIO modems until the XM301 and SX212 in 1986/86. The Atari 1030 modem was lame. This meant you really need an 850 interface to connect an industry-standard modem, such as something from Hayes. Since going online was pretty expensive in the 80s, I suppose that anyone that was able to afford a modem and associated online service costs was not concerned with the additional cost of the 850.

A recently-acquired Atari haul included an 850 interface module, so now I have one in my collection.

The 850 interface had four 9-pin serial ports on the side, although I’m not sure why you’d need so many. It also had a single parallel port and two SIO ports (so it could be daisy-chained to other peripherals such as a a disk drive). It also requires its own power via an external power supply.

The parallel interface is not the large 25-pin connector that I am familiar with from my Atari ST. Instead it is a smaller 15-pin connector that likely would have required an adapter or different cable. I think something like this would have worked:

I think my Dad might still have a couple old parallel printers in the basement. I’m not sure if they work, but it might be fun to find out if I can connect them with this. Still, I think an 850 would have been overkill if you only wanted a printer. For that there were other options.

Connecting a Printer

A printer was a popular peripheral back then. Of course, you could certainly get an Atari printer with an SIO connector, but the Atari dot-matrix printers were not great, usually rather noisy and slow with limited graphics capabilities. People instead wanted something better. The Star Gemini printer, a lower-cost Epson compatible, was popular and we had its successor, the Star SG-10 printer.

As I recall the SG-10 was about $300 in 1985 (about $930 in 2026). Of course, the SG-10 used a standard parallel interface, so it could not connect to our Atari 800XL. Fortunately, the 3rd party market had solved this problem. There were a variety of relatively low-cost printer interfaces you could buy for between $50 and $90 that made much more sense than getting an 850 interface module. These single-purpose devices had an SIO connector on one end and a parallel connection on the other. You’d connect the parallel cable to the printer and the device and then connect the device to your Atari.

We had the MPP 1150 interface, but there were others such as the Ape Face interface.

ICD MIO Board

Towards the end of the Atari 8-bit era, ICD released the MIO Board, for multi IO. It had serial and parallel ports like the 850, but also had a SCSI port for a hard drive and a built-in RAMdisk/print spooler. This highly coveted device is nearly impossible to find today.

Other Systems

The Atari ST used standard parallel and RS-232 so it didn’t need these interface boxes, just a simple cable would suffice.

I’m not familiar with the details of ports used by other 8-bit Commodore and Apple systems, so I’d love to hear from folks that used them back in the day. How did you connect peripherals to those computers?