Microsoft Open-Sources Bill Gates’ BASIC Code

Highlights

• Open-source release: Microsoft has made the source code for Microsoft BASIC for the 6502 Version 1.1 publicly available on GitHub.
• Historical significance: The code, written by Bill Gates and Ric Weiland, is considered a foundational piece of early personal computer software.
• Processor compatibility: The MOS 6502 processor was affordable and powered many iconic gaming systems and computers of its time.
• Preservation efforts: The open-sourcing allows the code to be preserved and explored, providing insights into early programming practices.

In the era of vibe coding, when even professionals are pawning off their programming work on AI tools, Microsoft is throwing it all the way back to the language that launched a billion devices. On Wednesday, the company announced that it would make the source code for Microsoft BASIC for the 6502 Version 1.1 publicly available and open-source. The code is now uploaded to GitHub under an MIT license (with a cheeky commit time stamp of “48 years ago”).

Microsoft called the code—written by the company’s founder, Bill Gates, and its second-ever employee, Ric Weiland—”one of the most historically significant pieces of software from the early personal computer era.” It’s pretty simple, clocking in at just 6,955 lines of assembly language, but that simplicity was key to its becoming so foundational to just about everything.

The MOS 6502 processor, which ran the code, was inexpensive and accessible compared to contemporary alternatives, and variations of the chip would eventually find their way into the Atari 2600, Nintendo Entertainment System, and Commodore computers. In fact, the story goes that Microsoft licensed its 6502 BASIC to Commodore for a flat fee of $25,000, which turned out to be a great deal for Commodore, which shipped millions of computers running the code.

Per Microsoft, the company’s first product was a BASIC interpreter for the Intel 8080, which was written by Gates and co-founder Paul Allen. The version the company dropped on GitHub is actually an updated version of BASIC, which contains bug fixes implemented by Gates and Commodore engineer John Feagans. While it’s called 1.1 on GitHub, Microsoft said it initially shipped as BASIC V2.

It’s kind of a big deal for Microsoft to finally open-source the entirety of the code, which was previously only available in bits and pieces. Without Microsoft’s official blessing to make this code public, it was possible that the original documentation, as well as the legal permission needed to use the code, would have been lost to history. Now it’s possible for the code to be preserved, played with, and better understood.

As Ars Technica points out, the assembly code can’t be run on modern devices directly, but is still functional in emulators and field-programmable gate array (FPGA) implementations that allow researchers and programmers to explore old code and mine it for everything from just understanding how it works to understanding how programmers of the past approached efficient design practices.

BASIC 5502 joins GW-BASIC, MS-DOS, and the Altair BASIC on the list of code that Microsoft has open-sourced in recent years.