Microsoft celebrated its 50th anniversary on April 4, 1975, and in honor of this milestone, Bill Gates made an announcement. He published the source code for the interpreter Altair Basic. Altair Basic was the first product released by Microsoft and was designed for the Mits Altair 8800 processors. The interpreter, which takes up less than 4 KB, was able to run on systems with just 4 KB of RAM.
Interestingly, when Bill Gates and Paul Allen were developing Altair Basic, they did not have an Altair 8800 computer to test it on. Instead, they utilized an Intel 8800 emulator on the PDP-10 system, to which they had access. The source code for Altair Basic is now available for download in the form of a pdf file, which is approximately 100 MB in size and contains scanned paper prints of the original assembler code.