Xerox Alto

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Xerox Alto
Xerox Alto mit Rechner.JPG
The Xerox Alto monitor has a portrait orientation.
Manufacturer Xerox PARC
Units sold 2,000
Media 2.5 MB single-platter cartridge
Memory 128-512 kB
Display 606x808 pixels
Related articles Xerox Star; Apple Lisa, Macintosh




The Alto was conceived 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. Industrial Design and manufacturing was sub-contracted to Xerox, El Segundo, whose Special Programs Group team included Doug Stewart as Program Manager, Abbey Silverstone Operations, Bob Nishimura, Industrial Designer. An initial run of 30 units was produced by Xerox, El Segundo (Special Programs Group), working with John Ellenby at Xerox PARC and Doug Stewart Xerox, El Segundo as well as Abbey Silverstone at Xerox El Segundo, who were responsible for re-designing the Alto’s electronics. Due to the success of the pilot run, the team went on to produce approximately 2,000 units over the next ten years.[7]




Alto uses a microcoded design but, unlike many computers, the microcode engine is not hidden from the programmer in a layered design. Applications such as Pinball took advantage of this to accelerate performance. The Alto has a bit-slice arithmetic logic unit (ALU) based on the Texas Instruments' 74181 chip, a ROM control store with a writable control store extension and has 128 (expandable to 512) kB of main memory organized in 16-bit words. Mass storage is provided by a hard disk drive that uses a removable 2.5 MB single-platter cartridge (Diablo Systems, a company Xerox later bought) similar to those used by the IBM 2310. The base machine and one disk are housed in a cabinet about the size of a small refrigerator; one additional disk can be added in daisy-chain fashion.

Alto both blurred and ignored the lines between functional elements. Rather than a distinct central processing unit with a well-defined electrical interface (e.g., system bus) to storage and peripherals, the Alto ALU interacts directly with hardware interfaces to memory and peripherals, driven by microinstructions output from the control store. The microcode machine supports up to 16 cooperative tasks, each with fixed priority. The emulator task executes the normal instruction set to which most applications are written (which is rather like that of a Data General Nova). Others tasks serve the display, memory refresh, disk, network, and other I/O functions. As an example, the bitmap display controller is little more than a 16-bit shift register; microcode moves display refresh data from main memory to the shift register, which serializes it into a display of pixels corresponding to the ones and zeros of the memory data. Ethernet is likewise supported by minimal hardware, with a shift register that acts bidirectionally to serialize output words and deserialize input words. Its speed was limited to 3 Mbit/s because the microcode engine could not go faster and continue to support the video display, disk activity and memory refresh.

Unlike most minicomputers of the era, Alto did not support a serial terminal for user interface. Apart from an Ethernet connection, the Alto's only common output device is a bi-level (black and white) cathode ray tube (CRT) display with a tilt-and-swivel base, mounted in "portrait" orientation rather than the more common "landscape" orientation. Its input devices are 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.


The keyboard is interesting in that each key is represented as a separate bit in a set of memory locations. As a result, it is possible to read multiple key presses simultaneously. This characteristic can be used to alter from where on the disk the Alto boots. The keyboard value is used as the sector address on the disk to boot from, and by holding specific keys down while pressing the boot button, different microcode and operating systems can 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.



The file manager program running on the Alto.



There was no spreadsheet or database software. (The first electronic spreadsheet program, VisiCalc, did not appear until 1979.)

Diffusion and evolution[edit]




In December 1979, Apple Computer's co-founder Steve Jobs visited Xerox PARC, where he was shown the Smalltalk-80 object-oriented programming environment, networking, and most importantly the WYSIWYG, mouse-driven graphical user interface provided by the Alto. At the time, he didn't recognize the significance of the first two, but was excited by the last one, promptly integrating it into Apple's products; first into the Lisa and then in the Macintosh, attracting several key researchers to work in his company.[13]


Xerox and the Alto[edit]


BYTE stated in 1981,[10]






Source code release[edit]

On October 21, 2014, Xerox Alto's source code and other resources were released from the Computer History Museum.[15]

See also[edit]


  1. ^
  2. ^ Koved, Larry; Selker, Ted (1999). "Room with a view (RWAV): A metaphor for interactive computing.". IBM TJ Watson Research Center. CiteSeerX: 


  7. ^ “The History of the Xerox Alto”. Carl J. Clement. March, 2002.
  10. ^ a b c Wadlow, Thomas A (September 1981). "The Xerox Alto Computer". BYTE. p. 58. Retrieved 19 October 2013. 
  11. ^ More significantly (and perhaps less controversially), it may be considered to be one of the first workstation systems in the style of single-user machines such as the Apollo, based on the Unix operating system, and systems by Symbolics, designed to natively run Lisp as a development environment. "Personal Computer Milestones". Blinkenlights Archaeological Institute. Retrieved 2006-12-31. 
  12. ^ Denber, Michel (February 1982). "Altos Gamesmen". BYTE (letter). p. 28. Retrieved October 19, 2013. 
  14. ^ a b Douglas K. Smith; Robert C. Alexander (2014). Fumbling the Future: How Xerox Invented, Then Ignored, the First Personal Computer. New York: William Morrow. 
  • Alto User's Handbook, Xerox PARC, September 2013

Further reading[edit]


External links[edit]