In 1975, Bill Gates and Paul Allen wrote the original Altair BASIC, with Monte Davidoff contributing the floating-point math routines. It was a remarkable piece of engineering that fit into just 4 kilobytes of memory.

As a new wave of affordable home computers emerged, powered by the inexpensive MOS 6502 processor, Microsoft adapted their BASIC. The 6502 port was released in 1976. Commodore licensed it for a one-time flat fee, integrating it deeply into their machines.

When you powered on a Commodore PET, VIC-20, or Commodore 64, the operating system did not boot to a desktop. It booted directly to the language itself. The blinking cursor after the word READY. was the first thing millions of people ever saw on a computer screen.

On September 3, 2025, Microsoft published this code on GitHub under the permissive MIT license, announced on the Microsoft Open Source blog. For decades only fragments and unofficial copies had circulated, mirrored on retrocomputing sites and kept in museum archives. This was the first official release.

Version 1.1 carries a small surprise. In one sense it is older than copies that had circulated for years, yet it already contains a garbage collector fix that Commodore identified and that was jointly implemented in 1978 by a Commodore engineer and Bill Gates. That fix shipped as the PET's BASIC V2.

Preservationists have since confirmed that the historical source can still produce byte exact builds. The release also fits a pattern: Microsoft open sourced MS-DOS 4.0 in 2024, and this follows GW-BASIC, which descended from the same lineage and later evolved into QBASIC and Visual Basic.

The source code and the announcement are gathered with the other materials in the Archive, so you can read the primaries for yourself.

It was not just an operating environment. It was an invitation.

A single, widely licensed interpreter introduced millions of people to programming. Commodore licensed the 6502 port for a flat fee of $25,000, a deal that put Microsoft software in front of a generation of new programmers and helped establish software licensing as a viable business in its own right.

Modern computers hide their complexity behind graphical interfaces. The 6502 machines booted directly into a programming language. They sat there, blinking patiently, waiting for you to tell them what to do. That simple READY. prompt taught a generation that computers were machines to be commanded, not just appliances to be consumed.

READY. is a museum exhibit about one small piece of software with an outsized legacy: Microsoft BASIC for the MOS 6502.

When the 6502 brought the price of a processor within reach of ordinary households, it was Microsoft BASIC that gave those machines a voice. It sat behind the startup banner on the Commodore PET, the VIC-20, and the Commodore 64, and the same lineage, licensed to Apple, became Applesoft BASIC on the Apple II. For millions of people, the blinking cursor after the word READY. was the first invitation a computer ever offered them. Type a line, press return, and the machine did exactly what you asked.

This exhibit exists to keep that history accessible, accurate, and easy to explore. We tell the story of how the software came to be, profile the machines it powered, look inside the code, and offer a few interactive demos so the experience feels less like reading a plaque and more like sitting down at the keyboard.

READY. is published by the Retro Software Foundation, a nonprofit dedicated to preserving and celebrating the software that shaped early personal computing.