Was DOS copied from CP/M?

August 06, 2016

CE8DC9FA-AE27-41DA-ACF3-37A98C4A41D1-August 06, 2016

Gary Kildall started Intergalactic Digital Research (later shortened to Digital Research or just DRI) and created the first microcomputer operating system, CP/M, used on many hobbyist personal computers before Apple and IBM introduced their machines. But Microsoft captured the microcomputer OS market, and with it the market for software applications, with its MS-DOS that came out years later for the IBM PC. For decades, a rumor has persisted that DOS was illegally copied from CP/M and that the fortune accumulated by Bill Gates rightfully belonged to Gary Kildall.

Several years ago, I did a forensic comparison of the binary code for MS-DOS to the source code for CP/M. I could find no signs of copying, and wrote a journal paper[9] and an article[10] about my examination. Since that time, the Computer History Museum in Mountain View, California received the source code for MS-DOS 2.0 from Microsoft and was given permission to make it public. The museum also received the source code for MS-DOS 1.1 from Tim Paterson, the original developer of DOS who was originally contracted by Microsoft to write MS-DOS. Comparing source code is more accurate than comparing binary code, which can produce false negatives, so I decided to perform another comparison to put the question to rest for good.

In addition to source code, I examined whether the DOS commands were copied from CP/M and whether the DOS system calls were copied from CP/M. These issues have also been discussed and debated for decades.

Finally, I will discuss whether DRI could have had a legitimate copyright claim against Microsoft.

The History
In 1980, IBM started a “skunk works” project in Boca Raton Florida to create a personal computer. This independent development group within IBM decided that they would focus on the hardware and partner with one of the small microcomputer companies already producing and selling programs. Thirty-six years ago, in August 1980, IBM executives flew to Bellevue, Washington to meet 24-year old Bill Gates who ran Microsoft, a company selling a very successful version of the BASIC programming language. Microsoft didn’t have an operating system, so Gates sent them to see his friend Gary Kildall at DRI in Pacific Grove, California, who had CP/M.[1][2][3][4][5]

At this point there are several versions of the story. In one version, Kildall and his team, described by some as a bunch of hippies, didn’t trust “Big Brother” IBM. Avoiding the meeting, Kildall took off in his plane for a joyride[1]. The IBM execs were met by Kildall’s wife and business partner Dorothy who refused to sign IBM’s non-disclosure agreement (NDA), a standard business document that would have kept the discussion secret. After several hours of quibbling over the NDA, not even getting to the essential negotiation, the IBM executives got frustrated and left[1][3][4][5].

In another version of the story, Kildall and DRI employee number 1, Tom Rolander, went off in Kildall’s plane to deliver software to a customer and put their chief negotiator Dorothy in charge[3]. Dorothy felt the NDA was too restrictive and their attorney Gerry Davis advised her to wait for Kildall to return[1][3]. Kildall returned later that day but again accounts differ as to whether he signed the NDA or even participated in discussions with IBM[1].

In any case, no deal was signed. The IBM negotiators flew back to Seattle that day and again met with Gates, still in need of an operating system. Gates decided to acquire the rights to Q-DOS from Seattle Computer Products for $75,000[6][7][8], and hired its author, Tim Paterson, to modify it into MS-DOS for licensing to IBM as PC-DOS.

The IBM PC became a huge success and Microsoft displaced DRI as the leading microcomputer operating system company. Kildall maintained that QDOS, and subsequently MS-DOS, had been directly copied from CP/M and thus infringed on his copyright. DRI attorney Gerry Davis claimed that forensic experts had proven that MS-DOS had been copied from CP/M and infringed DRI’s copyright but decided not to go to court[1].

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