Bill Gates and Paul Allen wrote a version of BASIC for the Altair 8800 in 1975.
The Altair 8800 was an early personal computer kit sold by Micro Instrumentation and Telemetry Systems, usually abbreviated MITS. Its appearance on the cover of Popular Electronics in January 1975 caught the attention of Gates and Allen, who believed a programming language could make the machine much more useful.
Allen demonstrated their BASIC interpreter to MITS in Albuquerque, New Mexico. MITS agreed to distribute it as Altair BASIC, giving the young company that became Microsoft its first major commercial product.
The computer is often confused with later machines such as the Apple II and IBM PC. Unlike those ready-to-use systems, the Altair 8800 was primarily sold as a kit and was operated through switches and lights.