In November 1980, Microsoft signed a contract to supply IBM with an operating system for its upcoming personal computer, despite not owning one. IBM had initially approached Gary Kildall’s Digital Research in August 1980 to license CP/M-86, a 16-bit operating system designed for Intel's 8088 microprocessor. When those negotiations failed, IBM turned to Microsoft, which had already agreed to supply a BASIC interpreter for the machine.
The 16-Bit Vacuum in Seattle
To fulfill its commitment to IBM, Microsoft turned to Seattle Computer Products, where engineer Tim Paterson had created an operating system named 86-DOS, originally dubbed QDOS. Paterson had written the software specifically because Digital Research’s 16-bit version of CP/M was delayed, leaving local hardware developers without a basic operating environment for 8086-based computers.
From Flat Fees to Boca Raton
In December 1980, Microsoft licensed 86-DOS from Seattle Computer Products for a flat fee of $25,000. Recognizing the strategic value of owning the operating system outright, Microsoft purchased all rights to the code the following summer for an additional $50,000. Paterson left Seattle Computer Products in 1981 to join Microsoft, relocating to Boca Raton, Florida, to work alongside IBM engineers preparing the hardware. When PC-DOS Version 1.0 shipped with the original IBM PC in August 1981, Paterson's assembly-language core consumed just 12 kilobytes of system memory.
Disputed Origins and Software Forensics
As the IBM PC gained widespread market adoption, disputes emerged over the origins of its operating system. Kildall claimed DOS copied CP/M, pointing to matching command interfaces and program calls. IBM offered both systems on the PC, but set CP/M's price at $240 while selling DOS for $40, driving most buyers to Microsoft's version. Meanwhile, Seattle Computer Products sued Microsoft over concealed IBM connections, settling out of court for nearly $1 million. Decades later, software forensic expert Bob Zeidman conducted a line-by-line source code examination of QDOS and CP/M, concluding that QDOS showed no evidence of code copying.
Expansion to the XT Core
In March 1983, Microsoft released DOS 2.0 alongside the hard-disk-equipped IBM PC-XT. A Microsoft team led by co-founder Paul Allen restructured the software to support hierarchical subdirectories and hard drives. Although these additions expanded memory usage to 28 kilobytes, the operating system maintained its low-overhead design as a simple command loader.
For fifteen years, Paterson's low-overhead assembly foundations remained the basic operating system standard beneath millions of personal computers worldwide.
AI-generated editorial illustration; not a documentary photograph.
Source: Microsoft MS-DOS early source code
SIGNAL TITANS
Leave a Reply