Exposed: Xerox Alto and CP/M OS source code released

The Computer History Museum has made the code behind yet more historic software available for download

Xerox Alto computer
Credit: flickr/Michael Hicks

Earlier this year I wrote about the source code for some classic proprietary software which has been made available to the public. Much of that code was released by or in conjunction with the Computer History Museum, which is a great source of this sort of stuff. Recently the museum has released yet more samples of classic source code, specially a host of programs related to the historic Xerox Alto computer, as well as some early versions of Digital Research’s CP/M operating system.

Xerox Alto source code

The Alto was a personal computer developed by Xerox at the Palo Alto Research Center (PARC) in the early 1970s. It was never sold commercially, but, according to former PARC employee Paul McJones writing about it for the Computer History Museum, about 1,500 were built and made available throughout Xerox. The Alto was a revolutionary computer, one of the first to feature a graphic display (a monitor with a 606x808 black and white display), keyboard, mouse and, for the time, a beefy amount of memory (128 KB) and hard disk storage (2.5 MB). It also introduced the concept of a computer desktop and featured the first Graphical User Interface. Xerox employees using Altos could access other local computers and services (such as a printer) that were networked via Ethernet; Altos were also connect to external networks using phone lines and radio links, such as those at other Xerox offices and ARPANET.

The released code, which you can download from the Computer History Museum website, is available for non-commercial use. It includes a range of software developed for the Alto such as the OS and associated utilities, PUP (PARC Universal Packet) a protocol for internetwork communications and Bravo, the first WYSIWYG editor. They’ve also released code for the four different programming languages the Alto supported: BCPL, Mesa, Smalltalk and Lisp. Documentation for all of the code is also included.

CP/M source code

In 1974, Gary Kildall, a consultant working part-time for Intel, set about creating a program for controlling then-new floppy disk drives. It quickly evolved into a new operating system for computers based on Intel’s 8080 microprocessor, which Kildall named CP/M (originally Control Program/Monitor, later Control Program for Microcomputers). It was revolutionary in that, unlike other operating systems of the time, it wasn’t written in hardware-specific assembly code, but instead in Kildall’s own PL/M language. This means that that the OS and programs written for it could, in theory, be ported to other computer hardware, greatly expanding their potential markets. CP/M also gave birth to some soon-to-be common conventions, such as 8 character file names with 3 character extensions. Kildall eventually founded Digital Research, Inc. to license CP/M and it quickly became the dominant OS for all personal computers until DOS came along in the early 1980s.

In honor of CP/M’s 40th birthday, the source code for a very early version from 1975, and three later versions from 1976, 1978 and 1979 are being made available for non-commercial use. The code can be downloaded download via the Computer History Museum’s website. The museum also provides access to release-specific documentation.

Have fun, classic software source code geeks!

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