CP/M

In 1972, Gary Kildall, then a consultant for Intel through his company Microcomputer Applications Associates, developed PL/M, a programming language designed for Intel microprocessors. This language, derived from the XPL language used for writing compilers, was the first high-level language specifically designed for microprocessor programming. The first substantial program written in PL/M was a text editor for the Intel 8008 microprocessor, which would later become CP/M’s ED editor (Control Program for Microcomputers).

In 1974, Kildall recognized the need for an operating system to exploit Shugart Associates’ new 8-inch floppy disk drives. That year, the dominant storage medium was punched paper tape, which cost approximately 100 times more than floppy disks for equivalent data capacity. Kildall proposed to Intel the development of a complete operating system including an editor, assembler, and loader, for $20,000. Intel declined the offer but provided Kildall with the necessary hardware to continue his development.

CP/M development took place in the workshop behind Kildall’s house at 781 Bayview Avenue in Pacific Grove, California. Unable to create alone the complex electronic interface between the microprocessor and the floppy disk drive, he called upon John Torode, a university friend teaching at Berkeley, who designed the necessary controller. In fall 1974, Kildall successfully ran CP/M for the first time, loading the system from paper tape to floppy disk and then booting the computer from it.

One of CP/M’s major innovations was its modular design separating hardware-dependent functions into a distinct component called BIOS (Basic Input/Output System). CP/M could thus easily adapt to different hardware configurations by modifying only the BIOS. The rest of the system, including the file manager and command interpreter, remained identical regardless of the platform. This portability proved decisive for CP/M’s commercial success.

In 1976, Gary and Dorothy Kildall founded Digital Research Inc. (initially named Intergalactic Digital Research) to commercialize CP/M. Initial sales were conducted from a rented office at 716 Lighthouse Avenue in Pacific Grove. CP/M floppy disks were sold for $70 each, and the couple went to the post office daily to collect checks resulting from advertisements placed in magazines such as Byte and Dr. Dobb’s Journal.

A licensing agreement with IMS Associates, Inc. in 1977 significantly increased CP/M’s credibility in the industry, making the system a standard adopted by most personal computer manufacturers of the era, including Altair, Amstrad, Kaypro, and Osborne. In 1978, revenue reached $100,000 per month and Digital Research moved into a Victorian house at 801 Lighthouse Avenue. By 1980, the company employed over 20 people and generated $3.5 million in revenue, five times that of Microsoft at the time.

In 1980, Bill Gates, who knew Kildall from discussions about a possible merger between their companies, recommended Digital Research to IBM for the operating system of its PC under development. Negotiations failed over confidentiality and business model issues: IBM wanted to purchase CP/M without royalties, while Digital Research preferred a per-copy-sold model. Microsoft seized this opportunity by purchasing a CP/M clone from Seattle Computer Products, renamed PC-DOS for IBM and MS-DOS for other manufacturers.

Faced with this situation, Kildall threatened IBM with a lawsuit for illegal copying of CP/M. IBM agreed to offer CP/M-86 as an option on the PC, but at $240 versus $40 for PC-DOS. This price difference massively steered the market toward PC-DOS/MS-DOS. Digital Research nevertheless continued to thrive for several years, developing multitasking operating systems for the IBM PC-XT and introducing graphical interfaces before Apple and Microsoft.

In the mid-1980s, MS-DOS’s dominance in the IBM-compatible PC market seriously affected Digital Research’s business. Gary Kildall, who never particularly enjoyed managing a large company, sold Digital Research to Novell in 1991. The assets were subsequently resold to Caldera in 1996, which would use DRI’s intellectual property in a lawsuit against Microsoft.

CP/M underwent major evolutions. MP/M (Multi-Programming Monitor) added multitasking and multi-user capabilities. CP/NET, introduced in 1980, connected CP/M computers to MP/M servers via various network protocols. A 16-bit version, CP/M-86, was developed for Intel 8086/8088 processors. However, the 8-bit version achieved the greatest success, with approximately 200,000 installations on over 3,000 different hardware configurations.

CP/M established fundamental concepts such as the separation between operating system and hardware through the BIOS, the use of standardized commands, and disk file management. These principles directly influenced MS-DOS’s design and, by extension, the evolution of personal operating systems. In 1995, the Software and Information Industry Association awarded Gary Kildall a lifetime achievement award, citing eight major contributions to the microcomputer industry. In 2014, the IEEE installed a commemorative plaque in front of Digital Research’s former headquarters, recognizing CP/M as an important milestone in personal computing history.

CP/M’s success illustrates the importance of open standards and software compatibility in the computer industry’s development. By enabling the development of a hardware-independent software ecosystem, CP/M helped transform microcomputers from specialized tools into general-purpose platforms accessible to all. This standardization fostered the emergence of an independent software market, foreshadowing the dominant economic model of the personal computer industry.