Almost half a century after its debut, Microsoft has released the source code for 6502 BASIC with an open license. The historic interpreter arrives for the first time officially and completely on a GitHub repository, so anyone can study, compile, or adapt it without legal restrictions.
The release clears decades of unofficial copies and scattered fragments, providing a canonical and documented version. The original header preserved in the code reads “BASIC M6502 8K VER 1.1 BY MICRO-SOFT”, a true time capsule that recalls how the company’s business was built before MS-DOS or Windows.
What exactly has Microsoft released?
This is the Microsoft BASIC version 1.1 for the 6502 microprocessor, dated mid-1978, and released under the permissive MIT License. The repository shares 6.955 lines of MOS 6502 assembly code, enabling downloading, modification, redistribution, and even commercial use if desired.
The source tree includes conditional compilation for several pioneer systems: Apple II (Applesoft), Commodore PET, Ohio Scientific (OSI) and the MOS KIM-1 kit, as well as a PDP-10 simulation environment for the 6502. As a historical reference, on GitHub itself there are timestamps that place the files “48 years in the Making".
Functionally, the interpreter offers full implementation of the BASIC language, floating-point arithmetic, string handling, array support (integer and string), input/output operations, and efficient memory strategies for 8-bit systems. It also incorporates chain garbage collector and dynamic storage of variables.
A pillar of home computing
The journey begins in 1975, when Bill Gates and Paul Allen wrote the company's first product: a BASIC interpreter for the Intel 8080 of the Altair 8800A year later, Gates and Ric Weiland adapted that foundation to the MOS 6502, giving birth to 6502 BASIC, which is now shared as open source.
In 1977, Commodore licensed the 6502 BASIC for a flat fee of $25.000. That agreement brought the interpreter to the Commodore PET and, later, to ecosystems that popularized home programming such as the VIC-20 and the legendary Commodore 64. It was the decade of writing lines like 10 PRINT "HELLO", 20 GOTO 10 and press RUN to see the magic.
In parallel, the same code trunk served as a basis for Applesoft BASIC on the Apple II, which replaced Steve Wozniak's Integer BASIC. Thus, a single source code family powered several key platforms in the birth of personal computing.
The MOS 6502 microprocessor powered iconic devices such as the Apple II and the Commodore series, as well as other machines and consoles with variants of the chip (Atari 2600 or NES). That they shared architecture does not imply that they ran this interpreter in those entertainment systems, but it explains why the community remains interested in their study and preservation.
Why publishing it as open source matters
For historians, teachers and enthusiasts, having a official licensed font, modern and clear It's pure gold. For years, preservationists have been rebuilding compilation environments and verifying that historical sources could generate ROMs byte by byte; now that work is consolidated with legal protection and verified materials.
The retro scene is experiencing a boom thanks to FPGA-based projects and emulation, where faithfully replicating 8-bit systems requires understanding their underlying software. Having open 6502 BASIC makes it easy to port, test, and revive classic hardware with a degree of authenticity that's difficult to achieve with partial recreations alone.
The Version 1.1 release includes the garbage collector fixes identified by Commodore and jointly implemented by John Feagans and Bill Gates In 1978, the same ones that reached users as PET BASIC V2. That is, the most representative edition of its actual use at the time is shared.
This movement links with previous publications of the house, such as that of GW-BASIC, which belongs to the same lineage of interpreters and eventually evolved into QBASIC and Visual Basic. The common thread is opening up key pieces of its legacy for study, education, and experimentation.
Anyone who wants to go deeper can go to official repository on GitHub, which also documents build targets for various systems and references community work (e.g., the use of modern toolchains like cc65) that makes it easier to build and run code on current environments.
Microsoft's gesture brings back to the forefront an interpreter that helped standardize programming in the early days of the PC. With MIT license, classic targets supported, and a database of 6.955 lines, the community now has a reliable reference for learning, experimenting, and preserving a fundamental piece of personal computing history.
