How Gary Kildall’s CP/M Lost the OS Crown to Bill Gates

In the early 1970s micro‑computers were a collection of isolated hardware platforms, each with its own I/O, disk formats, word length and byte order, making operating systems and applications non‑portable.

Gary Kildall, after graduating from the University of Washington and serving in the Navy, proposed an abstraction layer to hide hardware differences – the BIOS – and built a high‑level language PL/M for Intel’s 8008 CPU. Using PL/M he wrote CP/M, an operating system that ran on the BIOS rather than being tied to specific hardware, enabling easy porting across machines.

Intel did not adopt CP/M, only acquiring the PL/M language, so Kildall founded Digital Research in 1974 to sell CP/M. The OS quickly became the de‑facto standard, adopted by early personal‑computer makers such as Altair, Amstrad, Kaypro and Osborne.

When IBM decided to enter the PC market in 1980, it sought a ready‑made operating system. IBM’s negotiations with Digital Research broke down over a strict confidentiality agreement and a royalty‑per‑copy model that Kildall preferred, while IBM wanted a non‑exclusive license. After the talks stalled, IBM turned to Microsoft.

Bill Gates, having purchased the Quick and Dirty Operating System (QDOS) – a three‑month effort by 24‑year‑old Tim Paterson that cloned CP/M’s API – licensed it to IBM as PC DOS and retained the right to sell it elsewhere as MS‑DOS.

Microsoft’s strategy of pricing PC DOS at $40 while Digital Research sold CP/M for $240, combined with IBM’s focus on hardware volume rather than OS profit, caused MS‑DOS to eclipse CP/M and become the dominant operating system for the burgeoning PC‑compatible market.

Kildall later threatened legal action, claiming IBM had pirated CP/M, but IBM argued its OS agreement was non‑exclusive, allowing customers to choose CP/M or DOS. The episode illustrates how Kildall’s technical brilliance (BIOS, CP/M) was outmatched by Gates’s commercial acumen, ultimately shaping the foundation of the modern PC era.