Home Computer Archeology: Few early Microsoft products left as lasting a mark as 6502 BASIC. The interpreter introduced millions of people to computers and programming, shaping the next generation of software developers. Redmond is now releasing the original software, letting developers explore the code or even build something new from it.
A few months after releasing the Altair BASIC source code, Microsoft has shared another cornerstone of its early software success. The company announced that 6502 BASIC is now open source, giving programmers and archivists access to the official product after decades of relying on "unofficial" copies and fragments.
Microsoft recently released the code designed for the MOS Technology 6502 CPU, an influential 8-bit microprocessor introduced in 1975. A small team at MOS designed the 6502 as a simplified, less expensive, and faster alternative to the Motorola 6800.
Along with the Zilog Z80, the MOS chip formed the foundation for some of the most influential computing devices that fueled the home computer revolution in the early 1980s. The 6502 and its variants powered iconic machines such as the Atari 2600, Apple II, NES, Commodore 64, and many others.
Bill Gates and Ric Weiland ported 6502 BASIC from the original Altair version, and Commodore licensed it for a $25,000 flat fee, incorporating it into the VIC-20 and Commodore 64. Microsoft notes on the software's GitHub repository that the BASIC interpreter introduced millions of people to computers and programming through its approachable syntax.
Many programmers who later became leaders in the IT industry cut their teeth on Microsoft's BASIC, which became the de facto standard for computer programming. The 6502 version also played a key role in Microsoft's history, demonstrating the viability of software as a standalone business separate from hardware products.
Microsoft learned valuable lessons from porting BASIC to the 6502. The company notes that its multi-platform approach and development techniques later informed the creation of MS-DOS and Windows. The GitHub repository includes BASIC version 1.1, which incorporates additional fixes contributed by Commodore in 1978.
The new 6502 BASIC open source release took considerable effort to make happen. Microsoft collaborated with Michael Steil, who documented and rebuilt the original for multiple target systems. The GitHub release draws on Steil's work, providing the full BASIC interpreter in its most complete form.