Microsoft has released the source code for its Microsoft BASIC for the 6502 Version 1.1, making the historically significant software publicly available under an MIT license on GitHub. This code, originally written by Microsoft co-founder Bill Gates and early employee Ric Weiland, dates back nearly five decades.
The 6,955 lines of assembly language code powered the MOS 6502 processor, an affordable and widely used chip found in devices like the Atari 2600, Nintendo Entertainment System, and Commodore computers. Microsoft initially licensed the 6502 BASIC to Commodore for a flat fee of $25,000, leading to millions of shipped devices running this code.
Microsoft’s first product was a BASIC interpreter for the Intel 8080, developed by Gates and Paul Allen. The released version on GitHub represents an updated BASIC iteration with bug fixes contributed by Gates and Commodore engineer John Feagans. Although labeled as version 1.1 on GitHub, it originally shipped as BASIC V2.
This full open-sourcing marks a significant milestone, as the code was previously only available in fragments. Microsoft’s release ensures preservation and legal clarity, allowing enthusiasts and researchers to study, run, and experiment with the code through emulators and FPGA implementations.
Microsoft has also open-sourced other legacy code recently, including GW-BASIC, MS-DOS, and Altair BASIC.