Microsoft Puts Bill Gates’ Original 1978 6502 BASIC on GitHub

Anu Joy

Published on November 5, 2025

Microsoft revealed on Wednesday the source code for Microsoft BASIC for 6502 Version 1.1, the interpreter from 1978 that drove several systems through customised modifications, the Commodore PET, VIC-20, Commodore 64, and Apple II. Under an MIT license, which lets anyone freely use, change, and share the 6,955 lines of assembly language code the company shared on GitHub. The code that started the personal computer movement was quite important.

Writing the 6502 BASIC, Rick Weiland and Bill Gates, in 2010 on the Page Table blog said, “I (Bill Gates) included the WAIT command.” Different iterations of Microsoft’s BASIC interpreter defined many people’s first foray into programming in the late 1970s and early 1980s. Users can create an infinite loop of text on their screens by entering simple commands such as ‘10 PRINT HELLO’ and ‘20 GOTO 10’, often representing their initial exposure to straight computer control. Processing them one line at a time, the interpreter transformed these human-readable commands into executable directives for the processor.

There was an interaction between Microsoft’s low-level 6502 code with the processor utilising just 6,955 lines of assembly language which came as a major achievement. It was a win at a moment when RAM cost hundreds of dollars per kilobyte; Microsoft BASIC achieved amazing functionality within a small memory footprint. Price was most important in the emerging personal computer business. Priced at about $25, Chuck Peddle’s’s MOS 6502 processor running this BASIC was substantially less expensive than competitors, charging $200 for comparable chips.

Designer Chuck Peddle created the 6502 so as to make computers available to the masses, and manufacturers included different versions of the chip into millions of Commodore computers, as well as devices such as the Atari 2600 and high priced Nintendo Switch. Commodore ended up selling millions of computers loaded with Microsoft BASIC, even if $25,000 seemed to be a lot at the moment.