Want to build on Bill Gates? Microsoft open-sourced the original code written by the company founder - now it's over to you

• Microsoft has released 6,955 lines of BASIC assembly code from 1976
• Bill Gates and Ric Weiland adapted BASIC for the MOS 6502
• Commodore licensed Microsoft BASIC in 1977 for $25,000 worldwide

Nearly half a century after Bill Gates first began writing software that would launch Microsoft, the company has made that code public.

In early September, it placed the assembly source for its 6502 BASIC interpreter on GitHub, framing it as a historical milestone.

The release comes under the MIT License, meaning it can be freely studied, reused, or even sold.

Tracing BASIC from Altair to Commodore

For long-time observers, the gesture feels like both an act of preservation and a reminder of where Microsoft’s story began.

The 6502 interpreter dates back to 1976, when Gates and Microsoft’s second employee, Ric Weiland, adapted earlier work on BASIC for a new processor.

That adaptation was soon picked up by Commodore, which licensed it for $25,000 in 1977 and shipped it inside machines such as the PET, VIC-20, and Commodore 64.

Millions of these systems ended up in schools and homes, carrying Microsoft BASIC into classrooms where personal computing was still a novelty.

The code now released is version 1.1, which includes garbage collection fixes contributed jointly by Gates and Commodore engineer John Feagans in 1978.

On the Commodore PET, that update was known as BASIC V2, a version still remembered by many early adopters.

In practical terms, Microsoft has opened 6,955 lines of assembly language, complete with commit timestamps set “48 years ago.”

Beyond nostalgia, the source also shows how early interpreters were built to maximize scarce resources on 8-bit machines.

Microsoft notes that the release shows “conditional compilation support for multiple pioneering computer systems,” including the Apple II, Commodore PET, Ohio Scientific, and the MOS Technology KIM-1.

For historians and hobbyists, the most interesting elements are the techniques that made the interpreter usable on constrained hardware.

Among them are “Full BASIC language implementation,” “Floating-point arithmetic,” “String handling and manipulation,” and “Array support.”

The code also shows “Efficient memory utilization for 8-bit systems” and introduces “String garbage collection” and “Dynamic variable storage,” features that gave BASIC its reputation as a flexible beginner-friendly language.

The notes accompanying the release claim that BASIC positioned Microsoft “as a dominant force in personal computer software before MS-DOS or Windows.”

That’s true, but it omits the less flattering episodes that followed, such as how the company built MS-DOS with heavy inspiration from CP/M or how aggressive Windows licensing was later used against competitors.

Even with that context, the release remains notable. It provides transparency into a program that shaped Microsoft’s early fortunes and defined what beginner programming looked like in the late 1970s.

Via The Register

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