Xerox Alto

The Xerox Alto, developed in the Xerox PARC in 1973, was one of the first personal computers in history (although not the first), but it was the first one that used the desktop metaphor and a graphical user interface, as well as a mouse.

Architecture

The High was initially conceived in 1972 in an internal memorandum written by Butler Lampson and initially designed by Chuck Thacker. It had a bit-slice processor based on Texas Instruments 74181 chip, a ROM control storage with an expansion of writeable control storage and had 128 KB of expanded main memory at 512 KB, as well as a hard drive that used a 2.5 MB removable cartridge on a single plate of Diablo Systems (a company that later bought Xerox), similar to those used in the IBM 2310, all of it to a small cabinet size. The High Central Processing Unit (CPU) was an innovative microprogrammed processor that used microcode for most input/output operations, rather than hardware. The microcode machine performed 16 tasks, one of which performed the normal set of instructions (like the one of the Data General Nova), while the rest controlled the display, memory soda, disk, network and other input/output functions. For example, the display's bit map controller was little more than a 16-bit scroll record; the microcode was used to load the refraction information from the main memory display to the scroll record.

Other than an Ethernet connection, the Alto's only output device was a vertically mounted two-level (black and white) CRT (cathode ray tube) monitor. Its input devices were a keyboard, a three-button mouse, and an optional function keyboard (chord keyset). The concept of these last two elements was taken from the On-Line System of the Stanford Research Institute (SRI). While the mouse was an instant hit with Alto users, the function keyboard never caught on.

All the Alto's mice had three buttons. The first, mechanically operated, had two wheels perpendicular to each other. These were soon replaced by ball mice, invented by William English (engineer). Later optical mice were introduced, first with white light and later with infrared. The buttons on these ancient mice were elongated and arranged lengthwise rather than widthwise.

The keyboard was configured so that each key corresponded to a bit in a set of registers. This feature was used to change where the Alto was booted from. The keyboard registers were used as the disk address to boot from, and so by pressing a specific set of keys while pressing the home button, different microcodes and operating systems could be loaded. This gave rise to the expression "nose tear off" (nose boot), when the number of keys necessary to launch an operating system under test was greater than the number of fingers. This type of boot gave rise to "move2keys", a program that moved files on disk so that a certain key sequence could be used.

There were other peripherals for the Alto, such as a TV camera, a daisy wheel printer, and a parallel port, although they were fairly rare. The Alto could also control external drives, making it a file server. This was a fairly common application for this computer.

Software

The first programs for the Alto were written in the BCPL programming language and later in the Mesa language, which was not widely used outside of PARC, but which influenced several later languages, such as Modula. The Alto keyboard lacked the underscore key, its place being taken by the key for the left arrow character used in the Table language for the assignment operator. This feature of the Xerox Alto keyboard may have been the origin of the CamelCase style for compound identifiers (such as "ThisIsAVariable"). Another peculiarity of the Alto is that its microcode was programmable by the user.

El Alto helped popularize the use of the raster graphics model for all types of output, including text and graphics. It also introduced the concept of bit block transfer, or BitBLT, operation as the fundamental programming interface for the display. Despite its small memory size, a number of innovative programs were written for the Alto, including the first WYSIWYG document composition systems Bravo and Gypsy; graphics editors (bitmaps, printed circuit boards, integrated circuits, etc.); the first versions of the Smalltalk environment and one of the first multi-person network games.

Diffusion and evolution

From a technical point of view, the Alto was a small minicomputer, but it was more of a personal computer in the sense of having a single user sitting at the desk, when compared to mainframes and minicomputers of the time. It was never a commercial product, although several thousand units were manufactured. Several universities, including MIT, Stanford, CMU, and the University of Rochester, received donations from Altos including IFS servers and Dover laser printers. These machines were the inspiration for the Lilith workstations at ETH Zürich and the Three Rivers Company's PERQ; in addition to the Stanford University Network (SUN) workstation, which was finally brought to market by a spin-off type company, Sun Microsystems. The Apollo/Domain workstation and Apple's Lisa were also deeply influenced by the Alto.

The Xerox High was used to design the influential "D" series of Xerox workstations: Dolphin, Dorado and Dandelion. Also based on this design was a network router called “Eletra”. Dorado was a very fast ECL-based machine; Dolphin was a mid-range TTL-based machine originally designed to be the Star workstation. The original architecture for Dandelion, based on the AMD Am2900 of [bitslice microprocessor technology], was presented as the design called Wildflower and it was this low-cost design that would become the Star Xerox 8010 workstation.

Xerox created a product division (SDD) to commercialize PARC's work, initially using Dolphin as the basis for a workstation-type product. The Dandelion design became the Xerox 8010, which ran the Xerox Star software. The Star inspired Apple's Lisa and Macintosh personal computers, and helped popularize the graphical user interface on future personal computers and workstations.

These Xerox machines, especially the Alto, are rare today and are extremely expensive collector's items.