Microsoft publishes source code to Microsoft BASIC Version 1.1
This assembly language source code represents one of the most historically significant pieces of software from the early personal computer era. It is the complete source code for Microsoft BASIC Version 1.1 for the 6502 microprocessor, originally developed and copyrighted by Microsoft in 1976-1978.
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https://www.osnews.com/story/143274/microsoft-publishes-source-code-to-microsoft-basic-version-1-1/