Microsoft at 50: Bill Gates Shares the Code That Started It All

We are going to build the something new ?

Fifty years ago, two young dreamers—Bill Gates and Paul Allen—sat in a Harvard computer lab, hammering out code that would ignite a revolution. That code, written for the Altair 8800 minicomputer, became Microsoft’s first product: Altair BASIC. On April 2, 2025, as Microsoft approaches its 50th anniversary, Gates celebrated this milestone by releasing that original source code to the world. It’s a gift to tech enthusiasts, historians, and anyone curious about the humble beginnings of a company now worth $2.8 trillion. Here’s the full story of this historic moment, from its scrappy origins to its lasting legacy.

The Birth of a Giant: 1975 and the Altair 8800

Microsoft’s story begins in January 1975, when a 19-year-old Gates, a Harvard freshman, and his friend Paul Allen, then 22, spotted an article in Popular Electronics. It showcased the Altair 8800, a build-it-yourself minicomputer from Micro Instrumentation and Telemetry Systems (MITS), powered by Intel’s 8080 microprocessor. At the time, computers were hulking machines reserved for corporations and universities. The Altair, priced at $395 as a kit, promised something radical: personal computing.

Gates and Allen saw an opportunity. They called MITS’ CEO, Ed Roberts, claiming they’d built a version of BASIC—a programming language invented in 1964 at Dartmouth—that could run on the Altair. The truth? They hadn’t written a single line of code yet. Fueled by ambition and caffeine, they spent the next two months coding on Harvard’s PDP-10 mainframe, adapting BASIC for a machine they’d never touched. Their creation, Altair BASIC, was a success. On April 4, 1975, they founded “Micro-Soft” in Albuquerque, New Mexico, dropping the hyphen soon after. The personal computing era had begun.

The Altair 8800, the machine that inspired Microsoft’s first product.

The Code That Changed the World

The source code Gates released this week is the original Altair BASIC, written in Intel 8080 assembly language. Spanning 157 pages, it’s now available as a PDF on Gates Notes, his personal blog. This isn’t polished software—it’s a raw, teletype-printed relic from 1975, complete with faded ink and handwritten notes. Gates calls it “the coolest code I’ve ever written,” a sentiment that reflects both nostalgia and pride.

Altair BASIC wasn’t just a technical feat; it was a gateway. It let hobbyists program the Altair 8800, turning a box of circuits into a tool for creativity. The code itself is a dense mix of assembly instructions—think MOV, ADD, and JMP—tailored to the 8080’s 4 KB of memory. For modern readers, it’s a time capsule, not a plug-and-play app. To run it today, you’d need an emulator or a restored Altair, but its historical value is priceless.

Gates’ Reflections on 50 Years

Gates and Allen in Microsoft’s early days, dreaming big.

In his Gates Notes post, Gates described Microsoft’s milestone as “bittersweet.” Paul Allen, his co-founder and friend, passed away in 2018, leaving Gates to mark this anniversary alone. “I wish Paul were here to celebrate with me,” Gates wrote. He recalled their late-night coding sessions and their bold vision: “a computer on every desk and in every home.” That dream, once audacious, now feels quaint in a world of smartphones and cloud computing.

Gates also tied this release to his memoir, Source Code: My Beginnings, published in February 2025. The book details his early life, his partnership with Allen, and the founding of Microsoft. Releasing the Altair BASIC code feels like a companion piece—a tangible artifact to match the memoir’s personal narrative. At 69, with a fortune of $108 billion, Gates marveled at Microsoft’s journey: “Fifty years is a long time. It’s crazy that the dream came true.”

Microsoft’s Evolution: From BASIC to AI

Microsoft’s headquarters today, a far cry from its Albuquerque origins.

From that first product, Microsoft grew into a titan. MS-DOS and Windows made it a household name, while Office and Xbox expanded its reach. Under Satya Nadella, who succeeded Steve Ballmer in 2014, the company pivoted to cloud computing (Azure) and AI (Copilot), reclaiming its spot as a tech leader after missing the mobile wave. Today, it’s the world’s second-largest company by market cap, trailing only Apple.

The Altair BASIC release is a nod to those roots—a reminder that Microsoft’s empire started with two kids and a hunch. It’s not just nostalgia; it’s a testament to how far technology has come. Gates praised Nadella and the thousands of employees who’ve shaped Microsoft, calling its 50-year run “an amazing group effort.”

How to Explore the Code

The teletype that printed Microsoft’s first code, now a museum piece.

You can download the Altair BASIC source code from Gates Notes. It’s a PDF scan, not editable text, so don’t expect to copy-paste it into a compiler. For a deeper dive, check out annotated disassemblies of later versions like Altair BASIC 3.2, available online. Gates’ blog also includes rare photos—think teletype machines and shaggy-haired coders—adding flavor to this blast from the past.

Why This Matters.

Releasing the Altair BASIC source code isn’t about rewriting history—it’s about sharing it. For coders, it’s a chance to peek at the DNA of modern software. For the rest of us, it’s a story of grit and vision, a reminder that today’s tech giants started small. As Microsoft turns 50 on April 4, 2025, Gates’ gift celebrates not just a company, but an idea: that a few lines of code can change the world. Happy anniversary, Microsoft—and thank you, Bill Gates, for letting us look under the hood.