Microsoft open-sources 6502 BASIC from 1976

Microsoft open-sources 6502 BASIC

Microsoft has published the assembly-language source for its 6502 version of BASIC, originally written in 1976 by Bill Gates and Ric Weiland, and now available on GitHub.

The MOS 6502 CPU powered landmark machines like the Apple II, Commodore PET/VIC-20/C64 family, Atari consoles and even inspired designs in hobbyist consoles. Microsoft’s BASIC for the 6502 helped standardize early personal computing and teaching—think of a generation typing 10 PRINT "HELLO" and 20 GOTO 10 to learn programming.

For years hobbyists and preservationists reconstructed build environments and confirmed that historical sources could reproduce byte-exact ROMs. Microsoft’s release brings a clear, modern open-source license to that work and follows an earlier GW-BASIC release from the IBM PC lineage.

Why this matters now

Open-sourcing 6502 BASIC is more than nostalgia. It gives museums, universities, and developers a legally clear artifact to study, emulate, teach, and incorporate into preservation collections. It also helps reproducibility: researchers can verify builds and compare historical behavior against emulators or FPGA re-creations.

Because the code is now licensed openly, commercial teams building retro-inspired products or educational platforms can assess reuse without ambiguous provenance. For archivists, a modern license simplifies cataloging and public display.

Who benefits and how

These are practical uses that follow the release:

• Museums and archives can verify and display byte-exact ROMs with clear licensing.
• Educators can use original source to teach low-level programming and computing history.
• Engineers and retro game developers can audit and adapt code for emulation or FPGA projects.
• Researchers can compare historical implementations and build reproducible experiments.

Next steps for teams

If your organization maintains an archive, teaches systems programming, or builds retro-inspired products, the source is now a provable asset. Start by cloning the repository, validating a historical build, and documenting behavior differences between emulators and real hardware.

For preservation work, aim for byte-exact reproduction and a recorded build process. For education, pair the code with guided labs that show how assembly maps to BASIC semantics. For product teams, document licensing and perform risk checks before reuse.

Microsoft’s move wraps decades of hobbyist reconstruction in a clearer legal framework and reignites practical work on emulation, teaching, and archival authenticity. The complete source is available on GitHub for anyone ready to explore the roots of personal computing.