Technologies that Didn’t: ARCnet

In the late 1980’s, I worked at a small value added reseller (VAR) around New York City. While we deployed a lot of thinnet (RG58 coax based Ethernet for those who don’t know what thinnet is), we also had multiple customers who used ARCnet.

Back in the early days of personal computers like the Amiga 500, the 8086 based XT (running at 4.77MHz), and the 8088 based AT, all networks were effectively wide area, used to connect PDP-11’s and similar gear between college campuses and research institutions. ARCnet was developed in 1976, and became popular in the early 1980’s, because it was, at that point, the only available local area networking solution for personal computers.

ARCnet was not an accidental choice in the networks I supported at the time. While thinnet was widely available, it required running coax cable. The only twisted pair Ethernet standard available at the time required new cables to be run through buildings, which could often be an expensive proposition. For instance, one of the places that relied heavily on ARCnet was a legal office in a small town in north-central New Jersey. This law office had started out in an older home over a shop in the square of a smaller town—a truly historic building well over a hundred years old. As the law office grew, they purchased adjacency buildings, and created connecting corridors through closets and existing halls by carefully opening up passages between the buildings. The basements of the buildings were more-or-less connected anyway, so the original telephone cabling was tied together to create a unified system.

When the law office decided to bring email and shared printers up on Novell Netware, they called in the VAR I worked for to figure out how to make it all work. The problem we encountered was the building had been insulated at some point with asbestos fiber filling in the walls. Wiring on the surface of the walls and baseboards was rejected because it would destroy the historical character of the building. Running through the walls would only be possible if the asbestos was torn out—this would be removing the walls, again encountering major problems with the historical nature of the building.

The solution? ARCnet can run on the wiring used for plain old telephone circuits. Not very fast, of course; the original specification was 2.5Mbit/s. On the other hand, it was fast enough for printers and email before the days of huge image files and cute cat videos. ARCnet could also run in a “star” configuration, which means with a centralized hub (which we would today call a switch), and each host attached as a spoke or point on the star. This kind of wiring had just been introduced for Ethernet, and so was considered novel, but not widely deployed.

ARCnet deployed to well over ten thousand networks globally (a lot of networks for that time period), and then was rapidly replaced by Ethernet. The official reason for this rapid replacement was the greater speed of Ethernet—but as I noted above, most of the applications for networks in those days did not really make use of all that bandwidth, even in larger networks. Routers were not a “thing” at this time, but you could still connect several hundred hosts onto a single ARCnet or Ethernet segment and expect it to work with the common traffic requirements of the day.

At the small VAR I worked at, we had another reason for replacing ARCnet: it blew up too much. The cables over which POTs services run is unshielded, and hence liable to induced high voltage spikes from other sources. For instance, we had to be quite intentional about not using a POTs lines located within a certain distance of the older wiring in the buildings where it was deployed; a voltage spike could not only cause the network to “blank out” for some amount of time, it could actually cause enough voltage on the wires to destroy the network interface cards. We purchased ARCnet interface cards by the case, it seemed. After any heavy thunderstorm, the entire shop went from one ARCnet customer to another replacing cards. At some point, replacing cases of interface cards becomes more expensive than performing asbestos mitigation, or even just running the shielded cable Ethernet on twisted pair requires. It becomes cheaper to replace ARCnet than it does to keep it running.

An interesting twist to this story—there is current work in the Ethernet working group of the IEEE to make Ethernet run on … the cabling used for very old POTs services. This is effectively the same use case ARCnet filled for many VARs in the late 1980’s. The difference, today, is that much more is understood about how to build electronics that can support high voltage spikes while still being able to discriminate a signal on a poor transmission medium. Much of this work has been done for the wireless world already.

So ARCnet failed more because it was a technology ahead of its time, in terms of its use case, but in line with its time, in its physical and electronic design.