In the present day, we’re opening the vault—for actual.
For many years, fragments and unofficial copies of Microsoft’s 6502 BASIC have circulated on-line, mirrored on retrocomputing websites, and preserved in museum archives. Coders have studied the code, rebuilt it, and even run it in trendy methods. In the present day, for the primary time, we’re opening the hatch and formally releasing the code below an open-source license.
Microsoft’s first merchandise: From the Altair to the Commodore 64
Microsoft BASIC started in 1975 as the corporate’s very first product: a BASIC interpreter for the Intel 8080, written by Invoice Gates and Paul Allen for the Altair 8800. That codebase was quickly tailored to run on different 8-bit CPUs, together with the MOS 6502, Motorola 6800, and 6809. You’ll be able to be taught extra about this time and listen to instantly from Invoice Gates on the Microsoft Be taught Web site’s Historical past of Microsoft video sequence or by visiting Invoice Gates’ weblog.
The 6502 port was accomplished in 1976 by Invoice Gates and Ric Weiland. In 1977, Commodore licensed it for a flat payment of $25,000, a deal that positioned Microsoft BASIC on the coronary heart of Commodore’s PET computer systems and, later, the VIC-20 and Commodore 64. That call put Microsoft’s BASIC on the coronary heart of Commodore’s machines and helped hundreds of thousands of recent programmers be taught by typing:
10 PRINT “HELLO”
20 GOTO 10
That is BASIC M6502 8K VER 1.1, the 6502 BASIC lineage that powered an period of house computing and shaped the inspiration of Commodore BASIC within the PET, VIC-20, and the legendary Commodore 64. This very supply tree additionally incorporates variations for the Apple II (“Applesoft BASIC”), constructed from the identical core BASIC supply. The unique headers nonetheless learn, “BASIC M6502 8K VER 1.1 BY MICRO-SOFT”—a time capsule from 1978.
The model we’re releasing right here—labeled “1.1”—incorporates fixes to the rubbish collector recognized by Commodore and collectively applied in 1978 by Commodore engineer John Feagans and Invoice Gates, when Feagans traveled to Microsoft’s Bellevue workplaces. That is the model that shipped because the PET’s “BASIC V2.” It even incorporates a playful Invoice Gates Easter egg, hidden within the labels STORDO and STORD0, which Gates himself confirmed in 2010.
The enduring attraction of the MOS 6502 CPU
The MOS 6502 was the CPU behind the Apple II, Commodore 8-bit sequence, Atari 2600, Nintendo Leisure System, and lots of extra. Its simplicity, effectivity, and affect nonetheless encourage educators, hobbyists, and {hardware} tinkerers at this time.
In 2025, curiosity is as sturdy as ever. The retro-computing scene is prospering, with FPGA-based re-creations, emulator initiatives, and lively growth communities. The Commodore model has returned with the announcement of a brand new FPGA-powered Commodore 64the primary official Commodore {hardware} in a long time.
Reconstructing and preserving Microsoft BASIC
Through the years, devoted preservationists have reconstructed construct environments and verified that the historic supply can nonetheless produce byte-exact ROMs. Notably, Michael Steil documented and rebuilt the unique BASIC course of for a number of targets. He has ported the code to assemblers like cc65, making it potential to construct and run on trendy methods.
This open-source launch builds on that work, now with a transparent, trendy license. It follows Microsoft’s earlier launch of GW-BASICwhich descended from the identical lineage and shipped within the unique IBM PC’s ROM. That code developed into QBASIC, and later Visible Fundamental, which stays a supported language for Home windows software growth to today.
From the blinking cursor of 1977 to FPGA builds in 2025, BASIC nonetheless matches in your hand. Now, for the primary time, this influential 6502 model is really yours to discover, modify, and share.
Itemizing of Altair BASIC on show on the New Mexico Museum of Pure Historical past and Science.
“Altair Fundamental Signal” by Swtpc6800, public area by way of Wikimedia Commons.
Scott Hanselman
Vice President, Developer Neighborhood
Scott Hanselman is Vice President of Developer Neighborhood at Microsoft. A programmer, instructor, and speaker for 30+ years, he’s labored on .NET, Azure, and Developer Instruments. He hosts Hanselminutes, blogs at hanselman.com, and champions open supply, inclusion, and human-centered tech.
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Stacey Haffner
Director, Microsoft OSPO
Stacey Haffner is the Director of Microsoft’s OSPO and leads recreation developer advocacy. She is an engineer, recreation developer, and product chief who runs her personal indie studio, has constructed groups in startup environments, and now applies that experience to advancing open supply, empowering builders, and championing the sport dev neighborhood.
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