Microsoft has released the source code for the BASIC version it developed in 1976 for the MOS 6502 processor, a central component of many early home computers, The Register reports.

As far back as 1975, Bill Gates and Paul Allen developed Microsoft’s first product: BASIC for the Altair 8800 with the Intel 8080 processor. The following year, Gates and Ric Weiland ported the language to MOS 6502. In 1977, Commodore licensed the code for $25,000 and used it in its PET, VIC-20, and Commodore 64 computers. Millions of copies of these computers were sold, helping to popularize the home computer.

The now-published version 1.1 of the code consists of 6,955 lines of assembler and is available on GitHub under an MIT license. It contains a full BASIC implementation with support for floating-point arithmetic, string and array handling, math functions, input and output, and efficient memory usage for 8-bit systems.

The code also supports several classic computers, including the Apple II, Commodore PET, Ohio Scientific, and MOS KIM-1. “It even contains a playful Bill Gates Easter egg, hidden in the labels STORDO and STORD0,” according to a Microsoft blog post.