Mirror Review
April 4, 2025
Half a century ago today, a small company named “Micro-Soft” was founded by Bill Gates and Paul Allen with a bold vision: a computer on every desk and in every home. Today, as Microsoft turns 50 and celebrates its monumental 50th anniversary, co-founder Bill Gates marked the occasion by sharing a piece of history: the original 1975 source code for Altair BASIC, the company’s very first product.
Released yesterday via his “Gates Notes” blog as a 157-page scanned PDF of the original printout, Gates called it “the coolest code I’ve ever written to this day.” This simple BASIC interpreter, designed for the MITS Altair 8800 microcomputer kit featured on the cover of Popular Electronics magazine, wasn’t a code; it was the spark that ignited a software revolution and laid the foundation for the tech giant we know today.
While the code itself is a fascinating artifact, the story behind its creation is equally compelling. Here are 5 things you might not know about Microsoft’s foundational Altair BASIC:
1. Why BASIC? It Was All About the User (and Memory!)
In 1975, computing was far from user-friendly. Gates and Allen specifically chose to create a BASIC interpreter rather than a compiler. As Gates explained (referenced in outlets like The Register), an interpreter’s line-by-line approach gave instant feedback, allowing novice programmers on the Altair to easily spot and fix errors. This focus on usability for hobbyists was key. Furthermore, BASIC was relatively compact, crucial for fitting onto machines with extremely limited memory – the first version aimed for just 4 kilobytes!
2. The Two-Month Coding Sprint
Inspired by the January 1975 Popular Electronics cover, Gates and Allen famously contacted MITS founder Ed Roberts claiming they already had a working BASIC for his Altair. The reality? They didn’t. What followed was an intense, roughly two-month coding sprint. Gates focused primarily on the interpreter core, Allen handled development tools and utilities, and they brought in fellow Harvard student Monte Davidoff to write the vital, complex floating-point math routines. They worked tirelessly in Harvard’s computer labs on a DEC PDP-10 mainframe.
3. Coding Without the Computer
One of the biggest hurdles was that Gates and Allen didn’t actually have an Altair 8800, nor even its Intel 8080 processor chip, while writing the bulk of the code! To overcome this, Paul Allen wrote a remarkable piece of software: an emulator program that simulated the Intel 8080 microprocessor on the Harvard PDP-10. This allowed them to write, test, and debug their BASIC code before ever running it on the actual target hardware.
4. The Miraculous Paper Tape Demo
With the code finally complete (or close enough), Paul Allen flew to MITS headquarters in Albuquerque, New Mexico, carrying the program on a fragile punched paper tape. He had never run the software on a real Altair before. In a now-legendary moment, Allen loaded the BASIC interpreter from the paper tape into the Altair 8800, typed PRINT 2+2, and held his breath. The machine correctly responded: 4. It worked perfectly the first time, securing the crucial licensing deal with MITS.
5. It Formally Launched “Micro-Soft”
The successful MITS deal was the catalyst. Bill Gates noted, “This was a pivotal moment for Paul and me. Altair BASIC became the first product of our new company, which we decided to call Micro-Soft.” (The hyphen was later dropped). This single piece of software, born from a magazine cover and coded in a university lab, wasn’t just a technical achievement; it was the official commercial beginning of Microsoft.
A Foundation for the Future
Looking at the scanned pages of assembly code today offers a stark contrast to the complex operating systems, cloud platforms, and AI innovations Microsoft develops now. Yet, the principles embedded in Altair BASIC – understanding user needs, working within constraints, and sheer determination – remain relevant.
As Microsoft turns 50 today, the release of its “original source code” serves as a powerful reminder of its humble, yet audacious, beginnings, all sparked by two young enthusiasts, a magazine cover, and the “coolest code” Bill Gates ever wrote.
