- Microsoft has open-sourced its 1976 6502 BASIC interpreter.
- This BASIC interpreter was Microsoft’s very first product in 1975.
- Commodore licensed a version for its PET computers in 1977.
- The released code includes fixes jointly implemented by Microsoft and Commodore engineers.
For decades, code fragments and unofficial copies of Microsoft’s 6502 BASIC have been preserved online and in archives. Now, for the first time, this historic software is available under an open-source license.
Microsoft BASIC traces its origins back to 1975, as the company’s inaugural product: a BASIC interpreter designed for the Intel 8080. This initial version was famously written by Bill Gates and Paul Allen for the Altair 8800. The codebase was soon adapted for various 8-bit processors, including the MOS 6502, Motorola 6800, and 6809.
The specific 6502 port was finalized in 1976 by Bill Gates and Ric Weiland. A pivotal moment arrived in 1977 when Commodore licensed this version for $25,000. This agreement integrated Microsoft BASIC into the core of Commodore’s PET computers, and subsequently, the VIC-20 and Commodore 64.
The version being released, labeled “1.1,” incorporates crucial fixes to the garbage collector. These issues were identified by Commodore and jointly addressed in 1978. Commodore engineer John Feagans traveled to Microsoft’s Bellevue offices to collaborate with Bill Gates on these implementations. This particular version is the one that shipped as the PET’s “BASIC V2.”
The released code even contains a quirky Easter egg hidden within the labels STORDO and STORD0. Bill Gates himself confirmed its presence in 2010.
