The CP/M Microcomputer Operating System, 1974


Dr. Gary A. Kildall demonstrated the first working prototype of CP/M (Control Program for Microcomputers) in Pacific Grove in 1974. Together with his invention of the BIOS (Basic Input Output System), Kildall’s operating system allowed a microprocessor-based computer to communicate with a disk drive storage unit and provided an important foundation for the personal computer revolution.

Street address(es) and GPS coordinates of the Milestone Plaque Sites

36.623322, -121.923635, 801 Lighthouse Avenue, Pacific Grove, CA 93950 GPS: 36.623549,-121.923315

Details of the physical location of the plaque

The plaque will be mounted at the edge of the public sidewalk adjacent to a retaining wall surrounding the property.

How the intended plaque site is protected/secured

The plaque will be mounted flush with the surface of the sidewalk and securely embedded in the concrete.

Historical significance of the work

CP/M (Control Program for Microcomputers) was the first commercial operating system to allow a microprocessor-based computer to interface to a disk drive storage unit. CP/M played an important role in stimulating the hobbyist personal computer movement of the 1970s. Its ability to support software programs on a wide variety of hardware configurations enabled early use of microcomputer systems from many different manufacturers in business and scientific applications. Microsoft DOS, as licensed to IBM for the original PC, was written to emulate the "look and feel" of CP/M. Thus CP/M was the forerunner of the operating systems that now power the majority of the world’s computers and led to the personal computing revolution.

Features that set this work apart from similar achievements

Before Kildall’s development of CP/M, computer manufacturers provided proprietary applications software that worked only on their own hardware. All programs had to be written from the ground up to operate on each unique machine configuration. CP/M was initially designed to work on the Intel 8080 microprocessor and allowed computer systems built by any manufacturer who used that chip to run applications programs written by third-party suppliers. CP/M introduced a new element of competition into the computer marketplace that stimulated rapid growth in the use of low-cost systems in business, industry and academia and eventually in the home. According to Kildall, “CP/M was an instant success. By 1980, DRI had sold millions of copies of CP/M to manufacturers and end-users.”

Significant references

Kildall’s autobiography “Computer Connections” notes on page 55 that he solicited the help of John Torode in 1974. He gives no specific date but recalls that “This was in the late afternoon and … John and I retired to have a Chinese dinner in Pacific Grove”. E-mail correspondence from John, dated June 24, 2013, places the time frame as follows: “My wife and I concur that it was probably after our wedding on June 22 1974, but before we moved to Chicago (she worked for Bell Labs) in the fall”.

Kildall’s own public account of the history of CP/M was published in Dr Dobbs Journal in 1980: THE EVOLUTION OF AN INDUSTRY: ONE PERSON'S VIEWPOINT, "Dr. Dobb's Journal of Computer Calisthenics & Orthodontia", Vol.5, No.1, (January 1980) (number 41), page 6-7 [1]

Numerous popular accounts of the history of CP/M have been published in newspaper and magazine articles and in books, as well as online. Most of them focus on the fictitious story that DRI lost out to Microsoft on the IBM PC operating system decision because Kildall had taken the day off to go flying. Kildall refutes this story in “Computer Connections” but it is probably most eloquently recounted in Harold Evans’ book on U.S. pioneers and innovators “They Made America.” Harold Evans, “They Made America: Two Centuries of Innovators from the Steam Engine to the Search Engine” (2004) ISBN 0-316-27766-5 [2]

Steve Ham and Jay Greene, “The Man Who Could Have Been Bill Gates,” Bloomberg Business Week, 24 October 2004. [3]

Online only sources

CP/M and Digital Research Inc. (DRI) Web pages [4]

CP/M [5]

Gary Kildall Special (Video) [6]

A Short History of CP/M [7]

Gordon Eubanks Oral History (Computerworld 2000) [8]

Supporting materials

Numerous original documents, images, personal reminiscences, and videos contributed by employees are posted on the Digital Research Inc. page of the IT Corporate Histories Collection website hosted by the Computer History Museum at: