Xerox Alto

Xerox Alto

The Xerox Alto was an early personal computer developed at Xerox PARC in 1973. It was the first computer to use the desktop metaphor and graphical user interface (GUI).

It was not a commercial product, but several thousand units were built and were heavily used at PARC and at several universities for many years. The Alto greatly influenced the design of personal computers in the following decades, notably the Macintosh and the first Sun workstations. It is now very rare and a valuable collector's item.


The Alto was first conceptualized in 1972 in a memo written by Butler Lampson, inspired by the On-Line System developed by Douglas Engelbart at SRI, and was designed primarily by Chuck Thacker. Manufacturing was sub-contracted to Clement Designlabs, whose team included Carl J. Clement, Ken Campbell and Fred Stengel “The History of the Xerox Alto”. Carl J. Clement. March, 2002.] . An initial run of 80 units was produced by Clement Designlabs, working with Tony Ciuffini and Rick Nevinger at Xerox El Segundo, who were responsible for installing the Alto’s electronics. Due to the success of the pilot run, the team went on to produce approximately 2000 units over the next ten years .


The Alto had 128 (expandable to 512) kB of main memory and a hard disk with a removable 2.5 MB cartridge, all housed in a cabinet about the size of a small refrigerator. The Alto's CPU was a very innovative microcoded processor which used microcode for most of the I/O functions rather than hardware. The microcode machine had 16 tasks, one of which executed the normal instruction set (which was rather like a Data General Nova), with the others used for the display, memory refresh, disk, network, and other I/O functions. As an example, the bit map display controller was little more than a 16-bit shift register; microcode was used to fetch display refresh data from main memory and put it in the shift register.

Apart from an Ethernet connection, the Alto's only common output device was a bi-level (black and white) CRT display with a tilt-and-swivel base, mounted in "portrait" orientation rateher than the more common "landscape" orientation. Its input devices were a custom detachable keyboard, a three-button mouse, and an optional 5-key chord keyset. The last two items had been introduced by SRI's On-Line System; while the mouse was an instant success among Alto users, the chord keyset never became popular.

In the early mice, the buttons were three narrow bars, arranged top to bottom rather than side to side; they were named after their colors in the documentation. The motion was sensed by two wheels perpendicular to each other. These were soon replaced with ball-type mice, which were invented by Bill English; and eventually by optical mice — first using white light and then using IR.

The keyboard was interesting in that each key was represented as a separate bit in a set of registers. This characteristic was used to alter where the Alto would boot from. The keyboard registers were used as the address on the disk to boot from, and by holding specific keys down while pressing the boot button, different microcode and operating systems could be loaded. This gave rise to the expression "nose boot" where the keys needed to boot for a test OS release required more fingers than you could come up with. Nose boots were made obsolete by the "move2keys" program that shifted files on the disk so that a specified key sequence could be used.

Severral other I/O devices were developed for the Alto, including a TV camera, the Hy-Type daisywheel printer and a parallel port, although these were quite rare. The Alto could also control external disk drives to act as a file server. This was a common application for the machine.


Early software for the Alto was written in the BCPL programming language, and later in the Mesa programming language, which was not widely used outside PARC but influenced several later languages, such as Modula. The Alto keyboard was lacking the underscore key, which had been appropriated for the left-arrow character used in Mesa for the assignment operator. This feature of the Alto keyboard may have been the source for the CamelCase style for compound identifiers. Another feature of the Alto was that it was microcode-programmable by the user.

The Alto helped popularize the use of raster graphics model for all output, including text and graphics. It also introduced the concept of the "bit block transfer" operation, or BitBLT, as the fundamental programming interface to the display. In spite of its small memory size, quite a number of innovative programs were written for the Alto, including:
* the first WYSIWYG document preparation systems, Bravo and Gypsy;
* the Laurel e-mail tool, and its successor Hardy;
* the Sil vector grapics editor, used mainly for logic circuits, printed circuit board, and other technical diagrams;
* the Markup bitmap editor (an early paint program);
* the first WYSIWYG integrated circuit editor based on the Conway and Mead paradigm;
* the first versions of the Smalltalk environment
* one of the first network-based multi-person computer games (Alto Trek by Gene Ball).There was no spreadsheet or database software.

Diffusion and evolution

Technically, the Alto was a small minicomputer, but it could be considered a personal computer in the sense that it was used by a single person sitting at a desk, in contrast with the mainframes and other minicomputers of the era. It was arguably "the first personal computer", although this title is disputed by others [cite web
title=Personal Computer Milestones
publisher=Blinkenlights Archaeological Institute

The Alto was never a commercial product, although several thousand were built. Universities, including MIT, Stanford, CMU, and the University of Rochester received donations of Altos including IFS file servers and Dover laser printers. These machines were the inspiration for the ETH Zürich Lilith and Three Rivers Company PERQ workstations, and the Stanford University Network (SUN) workstation, which was eventually marketed by a spin-off company, Sun Microsystems. The Apollo/Domain workstation was heavily influenced by the Alto.

A trip to Xerox PARC by Apple Computer's Steve Jobs in 1979 led to the graphical user interface and mouse being integrated into the Apple Lisa and, later, the first Macintosh [cite web |title=PBS Triumph of the Nerds Television Program Transcripts: Part III|publisher=PBS (Public Broadcasting System)|url= |accessdate=2007-02-08 ] . Steve Jobs was shown the Smalltalk-80 programming environment, networking, and most importantly the WYSIWYG, mouse-driven GUI interface provided by the Alto.

In 1980–1981, Xerox Altos were used by engineers at PARC and at the Xerox System Development Department to design the Xerox Star workstations.

Xerox and the Alto

Xerox itself was slow to realize the value of the technology that had been developed at PARC cite book
author = Douglas K. Smith
coauthor = Robert C. Alexander
title = Fumbling the Future: How Xerox Invented, Then Ignored, the First Personal Computer
publisher = William Morrow
location = New York
year = 1988
] . After their unhappy experience with SDS (later XDS) in the late 1960s, the company was reluctant to get into the computer business again with commercially untested designs.

Before the advent of the IBM's Personal Computer, the computer market was dominated by costly mainframes and minicomputers equipped with dumb terminals that time-shared processing time of the central computer. Personal computers, like the early Apple models, were little more than toys for hobbists. So, through the 1970s Xerox showed no interest in the work done PARC. Even when the commercial success of the IBM PC in 1979 finally pushed Xerox to offer a PC of their own, they pointedly rejected the Alto design and opted instead for a very conventional model — with the then-standard 80 by 24 character-only monitor, and no mouse.

Xerox only realized their mistake in the early 1980s, after Apple's Macintosh revolutionized the PC market thanks to its bitmapped display and the mouse-centered interface inerface — both copied from the Alto . With the help of PARC researchers, Xerox eventually developed the Xerox Star office system, which included the Dolphin, Dorado and Dandelion workstations. These machines, based on the 'Wildflower' architecture described in a paper by Butler Lampson, incorporated most of the Alto innovations, including the graphical user interface with icons, windows, and folders, Ethernet-based local networking, and network-based laser printer services.

While the Xerox Star series was a relative commercial success, it came too late. The expensive Xerox workstations could not compete against the cheaper GUI-based workstations that appeared in the wake of the first Macintosh, and Xerox eventually quit the workstation market for good.

ee also

*Douglas Engelbart and NLS
*Alan Kay
*Apple Macintosh
*Apple Lisa
*Xerox Star

Further reading

* Michael A. Hiltzik, "Dealers of Lightning: Xerox PARC and the Dawn of the Computer Age" (HarperCollins, New York, 1999)


*"Alto User's Handbook", Xerox PARC, September 1979

External links

* [ Xerox Alto documents at]
* [ At the DigiBarn museum]
* [ Xerox PARC History page]
* [ An article on the Xerox Alto in Byte magazine]
* [ The Alto in 1974] Video
* [ A microcode-level Xerox Alto simulator]
* [ A lecture video of Butler Lampson describing Xerox Alto in depth. (length: 2h45m)]

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