Microsoft has officially opened the vault on one of its most iconic pieces of software history: the 6502 version of Microsoft BASIC. For years, enthusiasts, archivists, and retrocomputing fans had access only to scattered copies and unofficial fragments. Today, the code is being released under an open-source license—an unprecedented step for one of the programs that helped shape personal computing.

From Altair Beginnings to Commodore Classics

Microsoft BASIC traces its roots back to 1975, when Bill Gates and Paul Allen wrote their very first product: a BASIC interpreter for the Intel 8080 and the Altair 8800. Soon after, that interpreter was adapted for other 8-bit processors, including the MOS 6502, Motorola 6800, and 6809.

The 6502 port, completed in 1976 by Bill Gates and Ric Weiland, quickly gained traction. Just a year later, Commodore licensed it for a flat fee of $25,000. That move embedded Microsoft BASIC into the PET, VIC-20, and later the legendary Commodore 64, making it the programming language millions of beginners first encountered by typing:

This very release—BASIC M6502 8K VER 1.1—formed the foundation of Commodore BASIC. The same source code also powered Applesoft BASIC on the Apple II. In fact, original headers still read “BASIC M6502 8K VER 1.1 BY MICRO-SOFT”, a frozen artifact from the late ’70s.

Behind the Code: Fixes, Easter Eggs, and Collaboration

The open-source version being released is marked as “1.1”, a revision that included garbage collection improvements developed in 1978 by Bill Gates and Commodore engineer John Feagans. Feagans even visited Microsoft’s Bellevue offices to work alongside Gates on the fixes.

And, in classic Gates fashion, the code hides a small joke: playful labels named STORDO and STORD0, an Easter egg Gates later confirmed himself.

Why the 6502 Still Matters

The MOS 6502 processor isn’t just another relic of computing—it powered legends: the Apple II, Commodore series, Atari 2600, and even the Nintendo Entertainment System (NES). Its straightforward design and efficiency have kept it alive in classrooms, hobbyist projects, and emulators well into the modern era.

In fact, the retrocomputing scene is booming in 2025. Communities are building FPGA-based recreations, modern emulators, and even new official Commodore hardware—such as the recently announced FPGA-driven Commodore 64.

Preserving the Past, Inspiring the Future

For years, digital preservationists have carefully reconstructed build environments and proven that the old BASIC source can still produce byte-perfect ROMs. Michael Steil, for instance, documented the entire build process and ported the code to modern assemblers like cc65, making it possible to run the classic interpreter today.

Microsoft’s release builds on this groundwork by attaching a modern, open license. It follows the company’s earlier decision to release GW-BASIC, which eventually evolved into QBASIC and later Visual Basic—a language still supported for Windows app development.

From 1977 to 2025: BASIC Endures

What began as a blinking cursor on the PET in 1977 has carried through decades of innovation, from floppy disks to FPGA chips. Now, with the official open-source release of Microsoft’s 6502 BASIC, developers, historians, and curious tinkerers can not only revisit computing’s roots but also shape new projects inspired by them.

For the first time, the source code that taught millions their very first lines of code isn’t just preserved—it’s yours to explore, adapt, and share.