Personal Distributed Computing: The Alto and Ethernet Software 1 Personal Distributed Computing: The Alto and Ethernet Software1 Butler W. Lampson Systems Research Center Digital Equipment Corporation 1. Introduction A substantial computing system based on the Alto [58] was developed at the Xerox Palo Alto Research Center between 1973 and 1978, and was considerably extended between 1978 and 1983. The hardware base for this system is simple and uniform, if somewhat unconventional. The software, which gives the system its visible form and knits together its many parts, is by contrast complex, variegated, even ramified. It is convenient to call the whole complex of hardware and software “the Alto system”. This paper describes the major software components of the Alto sys-tem. It also tries to explain why the system came out as it did, by tracing the ideas that influenced it, the way these ideas evolved into the concept of personal distributed computing, and the nature of the organization that built the Alto. A companion paper by Chuck Thacker [56] describes the hardware. 1.1. Themes But a man’s reach should exceed his grasp, or what’s a heaven for? —Browning The Alto system grew from a vision of the possibilities inherent in computing: that computers can be used as tools to help people think and communicate [39]. This vision began with Lick-lider’s dream of man-computer symbiosis [32]. When he became head of the Information Proc-essing Techniques Office at ARPA, Licklider pursued the dream by funding the development of computer time-sharing. His successors, Ivan Sutherland, Robert Taylor, and Larry Roberts, con-tinued this work throughout the 1960s and extended it to computer networks. Taylor went on to manage the laboratory in which most of the Alto system was built, and people who worked on these ARPA projects formed its core. Their collective experience of time-sharing and networks became a major influence on the Alto design. Another important influence, also funded by ARPA, was Doug Engelbart. He built a revolu-tionary system called NLS, a prototype of the electronic office. In NLS all the written material handled by a group of people is held in the computer and instantly accessible on a display that looks something like an ordinary sheet of paper. He demonstrated this system at the 1968 Fall 1 This paper was presented at the ACM Conference on the History of Personal Workstations, Palo Alto, Jan. 1986. It appears in A History of Personal Workstations, ed. A. Goldberg, Addison-Wesley, 1988, pages 291-344. This version was made from the published version by scanning and OCR; it may have errors, and some slight changes have been made. Figures 2, 5 and 7 have been redrawn for clarity; the others are scanned. The 1972 memo describing the Alto project is at http://research.microsoft.com/lampson/38a-WhyAlto/Abstract.html.Personal Distributed Computing: The Alto and Ethernet Software 2 Joint Computer Conference in San Francisco [12,13]. NLS was too expensive to be practical then, but it made a profound impression on many of the people who later developed the Alto. Yet another ARPA project that had a strong influence on the Alto was Alan Kay’s Flex ma-chine, also called the Reactive Engine [21]. Kay was pursuing a different path to Licklider’s man-computer symbiosis: the computer’s ability to simulate or model any system, any possible world, whose behavior can be precisely defined. And he wanted his machine to be small, cheap, and easy for nonprofessionals to use. Like Engelbart, he attached great importance to a high-quality, rapidly changing display. He later coined the name “Dynabook” for the tool he envi-sioned, to capture its dynamic quality, its ubiquity, and its comfortable fit with people [22]. The needs of the Xerox Corporation also influenced the Alto, since Xerox provided the money that paid for it. In 1970 Xerox started a research center in Palo Alto called PARC to de-velop the “architecture of information” and establish the technical foundation for electronic of-fice systems that could become products in the 1980s. It seemed likely that copiers would no longer be a high-growth business by that time, and that electronics would begin to have a major effect on office systems, the firm’s major business. Xerox was a large and prosperous company with a strong commitment to basic research and a clear need for new technology in this area. To the computer people at PARC, this looked like a favorable environment in which to take the next step toward making computers into effective tools for thinking. The electronic office and the Dynabook, then, were the two threads that led to the Alto sys-tem. The idea of the electronic office is to do all the work of an office using electronic media: • capturing information, • viewing it, • storing and retrieving it, • communicating it to others, and • processing it. The idea of the Dynabook is to make the computer a personal and dynamic medium for han-dling information, which can model the world and make the model visible. Of course the Alto system is not an electronic office, or a Dynabook; these were ideals to draw us on, not milestones to be achieved (or millstones either). In the course of developing the Alto we evolved from these ideals to a new style of computing, which is the preferred style in the 1980s just as time-sharing was the preferred style of the 1970s; witness the conference for which this paper was prepared. For this style there is no generally accepted name, but we shall call it “personal distributed computing”. Why these words? The Alto system is personal because it is under the control of a person and serves his needs. Its performance is predictable. It is reliable and available. It is not too hard to use. And it is fast enough. In 1975 it was hard for people to believe that an entire computer is re-quired to meet the needs of one person. The prevailing attitude was that machines are fast and people are slow; hence the merits of time-sharing, which allows one fast machine to serve many of the slow people. And indeed time-sharing, with response times measured in seconds, is an ad-vance over a system that responds in hours. But this relationship holds only when the people are required to play on the machine’s terms, seeing information presented slowly and inconveniently, with only the clumsiest control over its form or content. When the machine is required to play the
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