ARCNET was developed by principal development engineer John Murphy at Datapoint Corporation in 1976 and announced in 1977.
A D V E R T I S E M E N T
It was the first LAN-based clustering solution, originally developed as an alternative to larger, more expensive computer systems.
The token-passing bus protocol of that I/O device-sharing network was subsequently applied to allowing processing nodes to communicate with each other for file-serving and computing scalability purposes. An application could be developed in DATABUS, Datapoint's proprietary COBOL-like language and deployed on a single computer with dumb terminals. When the number of users outgrew the capacity of the original computer, additional 'compute' resource computers could be attached via ARCNET, running the same applications and accessing the same data. If more storage was needed, additional disk resource computers could also be attached. This incremental approach broke new ground and by the end of the 1970s (before the first cassette-based IBM PC was announced in 1981) over ten thousand ARCnet LAN installations were in commercial use around the world, and Datapoint had become a Fortune 500 company. As microcomputers took over the industry, well-proven and reliable ARCNET was also offered as an inexpensive LAN for these machines.
Original ARCNET used RG-62/U coax cable and either passive or active hubs in a star-wired bus topology, a layout eventually copied by modern twisted pair Ethernet LANs. At the time of its greatest popularity ARCNET enjoyed two major advantages over Ethernet. One was the star-wired bus; this was much easier to build and expand (and was more readily maintainable) than the clumsy linear bus Ethernet of the time. Another was cable distance – ARCNET coax cable runs could extend 2000 feet (610 m) between active hubs or between an active hub and an end node, while the RG-58 ‘thin’ Ethernet most widely used at that time was limited to a maximum run of 600 feet (183 m) from end to end. Of course, ARCNET required either an active or passive hub between nodes if there were more than two nodes in the network, while thin Ethernet allowed nodes to be spaced anywhere along the linear coax cable, but the ARCNET passive hubs were very inexpensive. Passive hubs limited the distance between node and active hub to 100 feet (30 m). More importantly, the "interconnected stars" cabling topology made it easy to add and remove nodes without taking the whole network down, and much easier to diagnose and isolate failures within a complex LAN.