On Wednesday, Microsoft released the complete source code for Microsoft BASIC for 6502 Version 1.1, the 1978 interpreter that powered the Commodore PET, VIC-20, Commodore 64, and Apple II through custom adaptations. The company posted 6,955 lines of assembly language code to GitHub under an MIT license, allowing anyone to freely use, modify, and distribute the code that helped launch the personal computer revolution. “Rick Weiland and I (Bill Gates) wrote the 6502 BASIC,” Gates commented on the Page Table blog in 2010. “I put the WAIT command in.”
For millions of people in the late 1970s and early 1980s, variations of Microsoft’s BASIC interpreter provided their first experience with programming. Users could type simple commands like “10 PRINT ‘HELLO'” and “20 GOTO 10” to create an endless loop of text on their screens, for example—often their first taste of controlling a computer directly. The interpreter translated these human-readable commands into instructions that the processor could execute, one line at a time.
The version released—labeled 1.1—includes bug fixes implemented in 1978 by Commodore engineer John Feagans and Gates himself, including memory-management improvements that later shipped as “BASIC V2” on the Commodore PET.
The early personal computer market hinged on cost, with the MOS 6502 processor costing around $25. Variants of Microsoft BASIC helped put programmable microcomputing in reach for millions, as machines from Commodore and Apple competed on price rather than raw horsepower.
In a historic note, Commodore licensed Microsoft 6502 BASIC in 1977 for a flat $25,000, gaining perpetual rights to ship the software on unlimited machines—no royalties. Analysts note that per-unit licensing, as seen in later Microsoft products, could have generated tens of millions in revenue for the company had the terms been different.
