Bill Gates Reflects on the Code That Changed Everything — 50 Years Later

Bill Gates looks back at the 1975 code that kick-started Microsoft, calling it the spark that ignited personal computing.

Before Windows. Before Word. Before Microsoft became a household name, there was a teenage Bill Gates hunched over a keyboard, writing what he now calls "the coolest code I’ve ever written."

That code—an early version of BASIC—was written in 1975, before Gates ever dropped out of Harvard. It was designed to run on the Altair 8800, a do-it-yourself microcomputer that had just been featured on the cover of Popular Electronics. Gates and his childhood friend Paul Allen saw that article and immediately knew: this was the moment.

“We didn’t even have an Altair to test on,” Gates recalled. “We just believed it would work.” And it did. The BASIC interpreter they wrote became the first software for the Altair and laid the foundation for what would eventually become Microsoft.

From Dorm Room to Global Tech Titan

Fast forward to 2025. Gates, now 69, is looking back on that defining chapter as Microsoft gears up to celebrate its 50th anniversary. In a recent interview, Gates reflected on the early days: the adrenaline, the ambition, the late nights writing code without knowing whether it would run.

“That was the revolution,” he said. “That was the thing that ushered in personal computing.”

Gates’s reflections come just as he prepares to release a memoir titled Source Code: My Beginnings, in which he explores his early years, his passion for computing, and how a teenager’s dream turned into a multitrillion-dollar company.

A Legacy That Still Shapes the Industry

What started as a bold gamble became the foundation for much more—Word, Excel, PowerPoint, Windows, and eventually a sprawling software empire. Under current CEO Satya Nadella, Microsoft’s market cap now hovers around $2.8 trillion.

“Fifty years is a long time,” Gates said. “It’s crazy that the dream came true.”

He’s also marking another milestone: 25 years since stepping away from Microsoft’s top job to focus on the philanthropic foundation he started with his then-wife, Melinda. The Bill & Melinda Gates Foundation has since become one of the most influential nonprofit organizations in the world.

Still, it all started with a few hundred lines of code, written with no hardware, no company, and no guarantee it would work. Just two kids, a shared vision—and a whole lot of faith in the future.