John F. Shoch – Communications of the ACM

Research and Advances Mar 1 1982

The “worm” programs—early experience with a distributed computation

The “worm” programs were an experiment in the development of distributed computations: programs that span machine boundaries and also replicate themselves in idle machines. A “worm” is composed of multiple “segments,” each running on a different machine. The underlying worm maintenance mechanisms are responsible for maintaining the worm—finding free machines when needed and replicating the program for each additional segment. These techniques were successfully used to support several real applications, ranging from a simple multimachine test program to a more sophisticated real-time animation system harnessing multiple machines.

Architecture and Hardware

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Research and Advances Dec 1 1980

Measured performance of an Ethernet local network

The Ethernet communications network is a broadcast, multiaccess system for local computer networking, using the techniques of carrier sense and collision detection. Recently we have measured the actual performance and error characteristics of an existing Ethernet installation which provides communications services to over 120 directly connected hosts. This paper is a report on some of those measurements—characterizing “typical” traffic characteristics in this environment and demonstrating that the system works very well. About 300 million bytes traverse the network daily; under normal load, latency and error rates are extremely low and there are very few collisions. Under extremely heavy load—artificially generated—the system shows stable behavior, and channel utilization approaches 98 percent, as predicted.

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