Yesterday, with permission from Microsoft, Silicon Valley’s Computer History Museum published the source code for MS-DOS, the text-based operating system that ran so many personal computers in the ’80s and turned Microsoft into one of the industry’s dominant software companies. For computer geeks, the move can provide a bit of fun — a glimpse into how software was built in the past — and it provides a nice metaphor for a Microsoft that’s evolving with the times. Microsoft was once vehemently opposed to open source software, believing that it would cut into its core business, but in a modern world where open source is so very important, the company is changing its tune.

But the company shouldn’t stop at symbolic gestures. We love that the MS-DOS code is now available to the world at large (even if you can’t distribute your own changes to it, as with truly open source software). And we love that Microsoft has also released the code behind another seminal piece of software: Microsoft Word for Windows, originally released in 1990. But if the company is to regain its place at the head of the tech table, it needs to start open sourcing operating systems that are used today, not 30 years ago. Microsoft needs to open up the Windows Phone mobile OS — and maybe even desktop Windows.