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The Xerox Alto, developed at Xerox PARC in 1973, was the first personal computer and the first computer to use the desktop metaphor and graphical user interface (GUI). 1 Architecture
The Alto was first conceptualized in 1972 in an all points memo written by Butler Lampson. It had 128 (expandable to 512) Kbytes of main memory and a hard disk drive with a removable 2.5 Mbyte cartridge, all housed in a cabinet about as big as a small refrigerator. The Alto's CPU was essentially the same as the one used by the Data General Nova. This decision probably further cemented the 8-bit byte as a de-facto standard of computer memory measurement, as the Nova also used 8-bit bytes.
Apart from an Ethernet connection, the Alto's only common output device was a bi-level (black and white) CRT displayA computer display monitor or screen is a computer peripheral device capable of showing still or moving images generated by a computer and processed by a graphics card. Monitors generally conform to one or more display standards. As with television, sever, mounted in the "wrong" orientation (longest side vertical, portrait orientation). Its input devices were a custom keyboardA computer keyboard is a peripheral modelled after the typewriter keyboard. Keyboards are designed for the input of written text, and also to control the operation of the computer. Physically, computer keyboards are an arrangement of rectangular or near-r, a three- buttonFor other uses of the word button see Button (disambiguation). A button is a typically thin, small disc of hard substance, attached to a piece of cloth by stitches sewn through holes in its centre. The most common use of buttons is to secure the openings mouseA mouse is a handheld pointing device for computers, involving a small object fitted with one or more buttons and shaped to sit naturally under the hand. The underside of the mouse houses a device that detects the mouse's motion relative to the flat surfa, and an optional 5-key chord keyset . The last two items were borrowed from SRI's On-Line System; while the mouse was an instant success among Alto users, the chord keyset never became popular.
All Alto mice had three buttons. The earliest were mechanical and used two wheels perpendicular to each other. These were soon replaced with ball-type mice. Later, optical mice were introduced, first using white light and then using IR. The buttons on the early mice were narrow bars arranged top to bottom rather than side to side.
A number of other I/O devices were available 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.
2 Software
Early software for the Alto was written in the BCPL programming language, and later in the Mesa programming languageProgramming languages Mesa is a programming language developed at Xerox PARC that was used to program the Xerox Alto (one of the first personal computers with a graphical user interface), and later the Xerox Star workstations, and later the GlobalView des, 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 several WYSIWYG editors (for text documents, bitmaps, printed circuit boards, integrated circuits, etc.), and one of the first network-based multi-person computer games.
