Xerox Alto

The Alto was designed at Xerox PARC in early 1973 by a team led technically by Chuck Thacker, as an experiment: could a small machine on one desk replace facilities that until then required a large shared system? Butler Lampson had made the case the previous December in a memo titled "Why Alto?", arguing for building ten to thirty units. Alan Kay put part of his lab budget behind it. The first machines appeared on 1 March 1973.

It was the first computer to have the whole modern vocabulary at once: a bitmapped screen, overlapping windows, icons, a three-button mouse, WYSIWYG editing, Ethernet networking, and a networked laser printer to print what you saw.

The bitmap was the argument

A character terminal stores letters in fixed cells; it can only ever show you letters, in the places letters go. The Alto instead treated the screen as a grid of individually addressable dots and gave software direct control of every one of them. That single decision is what makes a graphical interface possible — icons, proportional type, drawings and text on one page, a cursor that can be any shape.

It was also expensive. The team noted that a full eight million bits of bitmap was more than they could afford in 1973, so they settled for far fewer, on the argument that a recognizable approximation of paper was worth more than fidelity. Nearly every interesting decision in this machine is of that form: what can we give up and still keep the feeling?

Where it came from, and where it went

The lineage is direct. The Alto was explicitly influenced by Engelbart’s NLS, and several of the people who built it — Bill English, Jeff Rulifson, Bill Paxton, Charles Irby, Bill Duvall — had come from SRI after the 1968 demo. It was also a rebuttal to the SDS 940: Lampson’s memo argued that time-sharing was the wrong shape for interactive work, and that each person should have a machine.

Xerox never sold it. Thousands were built and used inside Xerox and at selected universities, but no commercial Alto ever shipped, and the Xerox Star that followed in 1981 arrived expensive and late. The company realized the scale of the mistake in the early 1980s, when the Macintosh — bitmapped display, mouse-centred interface, both taken from the Alto — reorganized the personal computer market around ideas Xerox had owned outright for a decade.

Thacker received the Turing Award in 2009 for the Alto’s design; the 2004 Draper Prize went to Thacker, Kay, Lampson and Bob Taylor together. The Computer History Museum released the Alto source code in 2014, which is why this machine is unusually inspectable for a 1970s research computer — you can run it, rather than only read about it.