Microsoft Commemorates the Launch of Original DOS by Re-examining a Pivotal Release
As Microsoft unveils the original Disk Operating System (DOS), we take a moment to reflect on an event of perhaps greater significance.
Last year, in honor of Microsoft’s half-century anniversary, Bill Gates shared a fascinating artifact: the original Altair BASIC source code, presented as a 157-page PDF featuring scans of antiquated fan-fold paper.
This news was initially published in April 2025.
In a blog post heralding the release of this historic code, penned 50 years prior, Gates reminisced:
It feels like just yesterday that Paul (Allen) and I were hunched over the PDP-10 in Harvard’s computer lab, writing the code that would become the first product of our new company. That code remains the coolest code I’ve ever written to this day…
He elaborated on how witnessing the Altair 8080 gracing the cover of the January 1975 issue of Popular Electronics catalyzed their ambition:
The PC revolution was imminent, and we wanted to get in on the ground floor.
Subsequently, Gates contacted Ed Roberts, whose company, Micro Instrumentation and Telemetry Systems (MITS), produced the Altair kits.
Gates asserted he already possessed a version of BASIC for the 8080 microprocessor and was primed for collaboration. However, only the willingness to engage was accurate in his declaration.
To construct the BASIC interpreter, Paul Allen first had to devise an 8080 simulator on the college’s PDP-10.
Utilizing a book bought from a nearby bookstore—authored by Adam Osborne—he accessed the complete 8080 instruction set.
Implementing a BASIC interpreter through a simulator posed immense challenges, though the PDP-10’s enhanced resources proved advantageous.
Gates undertook the architecture of the interpreter; however, considerable cross-pollination undoubtedly occurred in their collaborative efforts.
Having previously designed a BASIC interpreter for the PDP-10, Gates could forgo theoretical consultation, allowing him to focus on the formidable task of compressing the language into just 4 kilobytes, while retaining sufficient space for executable programs.
Reflecting on this undertaking, Gates remarked in his blog post:
To meet that constraint, I used various techniques to optimize memory usage, like compact data structures and efficient algorithms.
It was a fun challenge, and although Paul and I were stressed about getting Altair BASIC to MITS as quickly as possible, I had a blast figuring out how to make everything fit.
The completed interpreter was submitted to MITS by Paul Allen on paper tape. Astonishingly, the program had not been tested on an actual 8080, let alone the Altair computer itself.
On route, Allen discovered they had neglected to create a bootstrap loader for the tape!
Any rational programmer would have deemed the likelihood of the tape functioning upon loading as nearly negligible; however, as illustrated in a brief video from over three decades ago, after a wobbly initial attempt, it astonishingly worked on the second try, leaving both Ed Roberts and Paul Allen in a state of astonishment!
To formalize their arrangement with MITS, a company needed to be established. Paul Allen conceived the name, merging Micro(processor) and Soft(ware), while Gates assumed the role of President, with Allen as Vice President.
This segment recounts the genesis of Microsoft. Now let us delve into the code itself—a compelling array of 157 pages, of which only a fragment is reproduced here:
It is astonishing to consider that this monumental achievement was the result of a trio—Gates, Allen, and Monte Davidoff, who crafted the mathematical framework, working tirelessly for two months.
The ingenuity embedded within the code marks a zenith of a bygone era—an era of hand-crafted, resource-limited programming.
Despite certain compromises, such as the exclusive use of integer arithmetic and single-letter variables, the endeavor remained formidable. Each command was encoded as a single-byte token, necessitating a myriad of space-saving stratagems.
Substantial insights can also be drawn from the accompanying comments. I was particularly intrigued by a nod to Bob Albrecht, a founder of the People’s Computer Company, who played a pivotal role in promoting the first Altair 8800 at the Homebrew Computer Club.
Albrecht also significantly contributed to the initiative aimed at establishing Tiny BASIC as a standard on numerous early machines. One of the comments reads:
IS IT BOB ALBRECHT RINGING THE BELL
FOR SCHOOL KIDS?
This refers to the Teletype input function and signifies a test for an ASCII Bell code (07). Indeed, their sole tool was the ASR33 teletype.
This comment likely stemmed from Bob Albrecht’s engagement in the free software movement and Tiny BASIC specifically.
Designed by Dennis Allison and the PCC in response to Gates’ open letter lamenting the pirating of Altair BASIC, Tiny BASIC emerged as a free version intended to mitigate Microsoft’s loss of royalties, which had exceeded $40,000.
Fast forward 50 years, and the transformation is staggering—Microsoft is now a resource-rich tech leader, advocating for open-source software, while Gates himself stands as a billionaire philanthropist, contributing his wealth to diverse causes.
In inviting enthusiasts to download the code, Gates concluded:
Computer programming has come a long way over the last fifty years, but I’m still super proud of how it turned out.
Source link: I-programmer.info.
