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CP/M: The Story of the OS That Almost Succeeded Over Windows


If it weren't for one fateful day in 1980, you might be using CP/M instead of Windows or Mac OS.

If you’re reading this, chances are you’re using a PC. It’s probably also running Windows, or maybe you’re using Mac OS X or Linux. If one fateful day in 1980 had played out differently, we might be using CP/M instead.


Gary Kildall was a computer scientist teaching at the Naval Postgraduate Academy in Monterey California in the early 1970s who caught wind of some new technology developed by Intel up north in Silicon Valley.

The company had recently introduced the microprocessor, but Kildall saw the full potential when Intel only saw it controlling traffic lights. He realized that it would be possible to build personal computers, but what they really needed was software to run them.

The Rise of CP/M

Kildall, working as a consultant for Intel, developed PL/M, or Programming Language for Microcomputers, which was a programming language for microcomputers, and Control Program for Microcomputers, or CP/M.

CP/M was an operating system that would theoretically run on any microcomputer, as long as the machine-dependent parts were ported.

Kildall’s design was brilliant. CP/M was divided into three parts: the BIOS (Basic Input/Output System), the Basic Disk Operating System (BDOS) and the Console Command Processor (CCP). The BIOS handled the machine-dependent code, while the CCP accepted commands from the user, similar to the shell on Unix and Linux systems.


Intel wasn’t really interested in CP/M, so he formed his own company, called Intergalactic Digital Research, later shortened to Digital Research. Like a lot of budding Northern California tech companies in the 1970s, Kildall and his wife Dorothy initially ran it out of their home, located in Pacific Grove.

CP/M, along with the S-100 bus using the Intel 8080 or Zilog Z-80 processor, became a de facto standard in the late ’70s. CP/M was useful because as long as developers coded in a machine-independent way, a CP/M program could run on almost any computer running CP/M without a programmer having to know how each machine worked. It was like a mini Unix in that regard.

It was so popular that there was even an add-on card, the SoftCard for the Apple II that allowed users to run it on their computers with 80-column text display (yes, that was a big deal back then.)

The company that made this card was a scrappy little startup based in Seattle called Microsoft.


The growing success of personal computers made IBM hungry for a piece of the action in 1980. The company decided to get into the market with its own PC. Big Blue usually designed entire computers by themselves, but figured that it would be too late with the company’s lumbering internal processes.

The company decided to do something completely unheard of for IBM. It would use off-the-shelf components and integrate them into a complete system.

CP/M was the obvious choice for the operating system, given how popular it was and how easy it was to port to other systems.

IBM initially approached Microsoft for CP/M, apparently thinking that they could license CP/M since they made the Apple II card. To its credit, Microsoft pointed IBM’s execs toward DRI down in California.

What happened next has been subject to endless speculation and an urban legend in the tech industry.

On the day when IBM showed up to negotiate with DRI, Kildall was delivering some documentation to a client using his private plane, leaving Dorothy and the company’s lawyers to hash out the deal. DRI apparently got stuck on the nondisclosure agreement after Kildall returned later in the day, and ultimately the deal came to nothing.

Desperate for an operating system, IBM turned to Microsoft. They found a CP/M clone written by a friend of Bill Gates, Tim Paterson of Seattle Computer Products and the designer of the SoftCard, dubbed QDOS, or “Quick and Dirty Operating System.” Microsoft licensed this to IBM so it would be ready in time.

Microsoft polished it and offered it to IBM as PC-DOS. The company convinced IBM to let them keep the rights to the operating system to license to other computer makers. IBM, confident that no one would clone the BIOS, the one piece of proprietary technology in the PC, agreed. (Since the computer you’re reading this on likely wasn’t made by IBM, it’s obvious how that turned out.)

Gary Kildall heard about the deal and threatened to sue IBM if it released PC-DOS. A deal was worked out where IBM would offer both systems, but IBM sold PC-DOS for $40, but CP/M-86, the PC version, was $240. It was hard to justify paying a higher price for what amounted to the same thing, and most people chose DOS. Most CP/M applications, such as the WordStar word processing system, were ported over to MS-DOS.

DRI Keeps Fighting

Despite the setbacks, DRI kept innovating. The company continued to innovate, creating a multitasking version of CP/M called MP/M.

When it was clear that DOS had eclipsed CP/M in terms of application support, DRI added MS-DOS compatibility and it evolved into DOS Plus and later DR DOS.

DRI also made inroads into the emerging world of the graphical user interface with GEM, which was best known as the GUI for the Atari ST line of computers.

Later Years

Even with the advances in technology, it was clear that DRI was no match for the Microsoft juggernaut. Digital Research was sold to Novell — the deal made Kildall very wealthy, but he never lived long enough to really enjoy his success. Sadly, Gary Kildall died in 1994 after injuries he suffered in a fall.

The legacy of Gary Kildall, Digital Research and CP/M still live on. DOS and later Windows still live in the shadow, including the way that drives are named.

The lesson is that established companies like DRI should always beware of smaller, hungrier companies like the Microsoft of 1980.

How might the industry have evolved with Gary Kildall at the helm instead of Bill Gates? Michael Swaine argued in a Dr. Dobb’s Journal article that it might have been much more collegial than competitive, owing to Kildall’s academic background.

Nevertheless, a lot of people still have strong memories of Gary Kildall and CP/M, with tribute sites. The PBS show The Computer Chronicles dedicated an episode to Kildall a year after his death. For a lengthy (1000-plus page) treatment of the early days of Silicon Valley, including Gary Kildall and Digital Research, you might want to track down a copy of the book “Fire in the Valley,” by Paul Freiberger and Michael Swaine.

Even though DRI, CP/M and even Gary Kildall are gone, they will definitely not be forgotten.


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David Delony

David Delony is a Bay Area expatriate living in Ashland, Oregon, where he combines his love of words and technology in his career as a freelance writer. He's covered everything from TV commercials to video games. David holds a B.A. in communication from California Sate University, East Bay.