Microsoft releases 6502 BASIC

Microsoft has officially released the source code of its historic 6502 BASIC interpreter from 1976 as open source for the first time, making an important contribution to preserving the history of home computers. The software was originally developed by Bill Gates and Ric Weiland for the popular 8-bit processor MOS 6502. It was later used as the basis for the influential Commodore PET, VIC-20 and Commodore 64 computers – Millions of users learned to program with it, and it still shapes the retro computing culture scene today.

According to Microsoft, version 1.1, which has now been released under the MIT license, includes improvements to memory management that were implemented in 1978 together with Commodore developer John Feagans. This is the version that was delivered as BASIC V2 on the PET and still lives in the ROM archives of computer museums and emulators today. The 6955 lines of assembly source code are now available on GitHub – including support for various historical systems such as Apple II or Commodore PET.

Also on board are the documented Easter Eggs from Bill Gates himself. Several hidden functions are concealed in the source code of Microsoft 6502 BASIC, including the famous STORDO and STORD0 labels, as Bill Gates himself confirmed in 2010. The WAIT 6502,1 command is particularly well-known, which causes the word MICROSOFT! to appear on the screen on a Commodore PET with BASIC V2 – Bill Gates had deliberately built in the hidden trademark.

With this release, Microsoft is emphasizing the historical significance of the BASIC interpreter for its own beginnings. At the same time, the company points out in its announcement that the community, from museum archives to modern FPGA and emulator projects, has been committed to its preservation and practical use for decades. In 2020, Microsoft had already published the GW-BASIC interpreter as open source, which dates back to 1983 and was used for IBM-compatible PCs and MS-DOS.

(fo)