Xerox Alto: Wikis


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Xerox Alto
Xerox Alto.jpg
The Xerox Alto monitor has a portrait orientation.
Manufacturer Xerox PARC
Release date 1973 (1973)
Units sold 2000
Media 2.5MB single-platter cartridge
CPU Bit-slice processor based on the TI 74181
Memory 128-512kB,
Input Keyboard, 3-button Mouse, 5-key chord keyset
Successor Xerox 820
Related articles Apple Macintosh

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, other Xerox facilities, 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 is 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 (NLS) 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 [1]. 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 [1].

Several Xerox Alto chassis are now on display at the Computer History Museum in Mountain View, California.


The Alto had a bit-slice processor based on the Texas Instruments' 74181 chip, a ROM control store with a writable control store extension and had 128 (expandable to 512) kB of main memory and a hard disk that used a removable 2.5 MB single-platter cartridge (Diablo Systems, a company Xerox later bought) similar to those used by the IBM 2310, 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 bitmap 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 rather 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. These were photo-mechanical mice — first using white light and then using IR to count the rotations of wheels inside the mouse.

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.

Several 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 lacked 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:

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. [2]

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.

The White House information systems department acquired an Alto, and sought to lead Federal computer suppliers in its direction. The EOP issued a request for proposal for a computer system to replace the aging OMB budget system, using Alto-like workstations, connected to an IBM-compatible mainframe. The request was eventually withdrawn because none of the mainframe companies could supply such a configuration.

In 1979, Apple Computer's founder Steve Jobs visited Xerox PARC, where he was shown the Smalltalk-80 programming environment, networking, and most importantly the WYSIWYG, mouse-driven graphical user interface provided by the Alto. He reportedly was not impressed by the first two, but was excited by the last one, and promptly integrated it — first into the Apple Lisa and then in the Macintosh, inviting several key researchers to work in his company [3].

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.[4] 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 personal computers, like the Apple II models with Visicalc, drove a disbelieving IBM to put their name on the derivative IBM PC, the computer market was dominated by costly mainframes and minicomputers equipped with dumb terminals that time-shared processing time of the central computer. So, through the 1970s, Xerox showed no interest in the work done at PARC. When Xerox finally entered the PC market, with the Xerox 820, they pointedly rejected the Alto design and opted instead for a very conventional model, a CP/M-based machine—with the then-standard 80 by 24 character-only monitor, and no mouse.

With the help of PARC researchers, Xerox eventually developed the Xerox Star (and later the cost reduced Star; the 6085) office system, which included the Dandelion and Daybreak 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, folders, Ethernet-based local networking, and network-based laser printer services.

Xerox only realized their mistake in the early 1980s, after Apple's Macintosh revolutionized the PC market thanks to its bitmap display and the mouse-centered interface—both copied from the Alto.[4] 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.

See also

Further reading

  • Hiltzik, Michael A. (1999). Dealers of Lightning: Xerox PARC and the Dawn of the Computer Age. New York: HarperCollins. ISBN 0887308910.  


  1. ^ a b “The History of the Xerox Alto”. Carl J. Clement. March, 2002.
  2. ^ "Personal Computer Milestones". Blinkenlights Archaeological Institute. Retrieved 2006-12-31.  
  3. ^ "PBS Triumph of the Nerds Television Program Transcripts: Part III". PBS (Public Broadcasting System). Retrieved 2007-02-08.  
  4. ^ a b Douglas K. Smith; Robert C. Alexander (1988). Fumbling the Future: How Xerox Invented, Then Ignored, the First Personal Computer. New York: William Morrow.  
  • Alto User's Handbook, Xerox PARC, September 1979

External links



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