Forty years ago today, on April 4, 1975, two friends from Seattle formed a partnership called “Micro-soft.”

In an email to Microsoft employees this week, marking the milestone, Bill Gates recalled the company’s original vision: “Early on, Paul Allen and I set the goal of a computer on every desk and in every home,” he wrote.

In reality, that’s only partially true. The company’s real goal was, “A computer on every desk and in every home, running Microsoft software.”

So in that spirit, here is one way to think about Microsoft’s goal in 2015: “An app on every device and in every pocket, running on Microsoft’s cloud.”

Microsoft has experienced dramatic change over the past year, led by Satya Nadella. The new CEO has pushed the company to loosen its grip on its past and think bigger. We’ve seen the early evidence of the new philosophy in decisions to make Office free on smartphones and tablets, to make the .NET platform open source, and to push Windows into new devices such as the HoloLens headset.

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There are hints of bigger changes to come, with one of the company’s top engineers saying this week that an open-source Windows is “definitely possible.”

Gates, who stepped down as CEO in 2000, as a full-time executive in 2008 and as chairman last year, remains a board member, adviser and major shareholder. In his email to employees on Friday, which was leaked via Twitter, he talked about the accelerating pace of change in the industry and the company.

I believe computing will evolve faster in the next 10 years than it ever has before. We already live in a multi-platform world, and computing will become even more pervasive. We are nearing the point where computers and robots will be able to see, move and interact naturally, unlocking many new applications and empowering people even more. Under Satya’s leadership, Microsoft is better positioned than ever to lead these advances. We have the resources and drive to solve tough problems. We are engaged in every facet of modern computing and have the deepest commitment to research in the industry. In my role as technical advisor to Satya, I get to join product reviews and am impressed by the vision and talent I see. The result is evident in products like Cortana, Skype Translator, and HoloLens-and those are just a few of the many innovations that are on the way. In the coming years, Microsoft has the opportunity to react even more people and organizations around the world. Technology is still out of reach for many people, because it is complex or expensive, of they simply do not have access. So I hope you will think about what you can do to make the power of technology accessible to everyone, to connect people to each other, and make personal computing available everywhere even as the very notion of what a PC delivers makes its way into all devices. We have accomplished a lot together during our first 40 years and empowered countless businesses and people to realize their full potential. But what matters most now is what we do next. Thank you for helping make Microsoft a fantastic company now and for decades to come.

In an industry as dynamic as this, the company’s existence for “decades to come” is certainly not guaranteed, but that’s what makes things interesting. And no matter your opinion of its strategy, or its ability to innovate, it’s hard to dispute that the company has become more interesting over the past couple years.

Happy Birthday, Microsoft.

Update: Here’s how Allen marked the anniversary on Twitter this morning.