The History of Windows: From a BASIC Interpreter to Windows NT
How Microsoft's 1975 founding led, eighteen years later, to hiring a DEC operating-system veteran to build Windows NT from scratch.
The Windows most people use today has a more direct engineering lineage than its branding suggests — it isn’t a descendant of the original 1985 Windows 1.0 at all. It comes from a separate operating system, built by a separate team, hired specifically because Microsoft needed something the original Windows architecture could never become.
Microsoft’s founding
Microsoft was founded on April 4, 1975, by Bill Gates and Paul Allen in Albuquerque, New Mexico, to sell a BASIC language interpreter Gates and Allen had written for the Altair 8800, an early hobbyist personal computer. The original Windows product line (Windows 1.0 in 1985, through Windows 3.1 and eventually Windows 95/98/Me) was a graphical shell running on top of MS-DOS — never a true, independent operating system with its own kernel, memory protection, or security model.
Why Microsoft needed something entirely different
Running on top of MS-DOS meant the DOS-based Windows line inherited MS-DOS’s fundamental limitations: no real memory protection between applications, no built-in multi-user security model, and general fragility under heavy or business-critical workloads. By the late 1980s, Microsoft needed a genuinely modern, portable, secure operating system to compete for business and server workloads — and building one from scratch meant hiring people who had already done exactly that, elsewhere.
Hiring Dave Cutler
Dave Cutler joined Microsoft from Digital Equipment Corporation (DEC) in October 1988. At DEC, Cutler had already designed several operating systems, including VMS — widely respected for its reliability and security model. At Microsoft, he was hired specifically to lead the design of a new, from-scratch operating system that would become Windows NT (“New Technology”).
The NT team started small — around 20 engineers in 1988 — and grew to roughly 150 by the time the first shipping version was ready, five years later.
Windows NT 3.1 ships
Windows NT 3.1 — the version number chosen to align with the contemporary consumer Windows 3.1, despite being an entirely separate codebase — shipped on July 27, 1993. It introduced real preemptive multitasking, proper memory protection between processes, a genuine security model (access tokens, discretionary ACLs — the same architecture covered elsewhere on this blog), and portability across CPU architectures beyond just Intel x86.
From “NT OS/2” to Windows NT: the Microsoft-IBM split
When Cutler’s team began work in 1988, the project wasn’t called Windows NT at all — it was OS/2 3.0 (later NT OS/2), the planned third version of the operating system Microsoft was co-developing with IBM as the intended successor to MS-DOS. The NT codename itself traces back to the original target hardware: an emulated version of Intel’s experimental i860 processor, internally code-named N10 (“N-Ten”). Everything changed after May 1990, when Microsoft shipped Windows 3.0 — a surprise commercial blockbuster that sold far beyond anything OS/2 had achieved. With Windows suddenly the more valuable brand and the more strategically important API to support, Microsoft rewrote the still-unreleased NT OS/2’s primary programming interface from an extended OS/2 API to an extended Windows API, effectively pivoting the entire from-scratch operating system project onto the Windows name. IBM, unwilling to follow, continued OS/2 development alone, and the Microsoft-IBM partnership that had produced OS/2 in the first place ended for good. What had started as an operating system for IBM’s platform shipped, three years later, as Windows NT 3.1 instead.
The VMS connection, and a persistent naming legend
Cutler didn’t come to Microsoft alone — several engineers who had worked with him at DEC on VMS, and on a cancelled next-generation DEC operating system project internally called Mica, joined alongside him. NT’s internal architecture (the kernel/executive split, the object manager, the design of its I/O subsystem) shows clear conceptual lineage from that VMS/Mica background, enough that DEC reportedly considered the resemblance seriously before the two companies settled matters commercially instead, as part of a broader technology relationship that also saw Microsoft port NT to DEC’s Alpha processor. This lineage fed a long-running piece of tech folklore: shift each letter of “VMS” forward by one in the alphabet and you get “WNT,” Windows NT’s own internal abbreviation. Cutler has acknowledged the pun, but the timeline complicates it as a genuine origin story — the project was still called NT OS/2, with no Windows branding at all, for most of its early development, which sits awkwardly with a joke that depends on the WNT initialism existing from the start. Microsoft’s own later explanation was more mundane: NT was simply expanded to stand for “New Technology” for marketing purposes, without any deeper acronym meaning intended.
Two product lines, one eventual merger
For most of the 1990s, Microsoft shipped two separate Windows lines in parallel: the consumer-facing DOS-based line (3.1, 95, 98, Me) aimed at compatibility and low hardware requirements, and the NT-based line (NT 3.1, 3.5, 4.0, 2000) aimed at business and server workloads where reliability mattered more than legacy DOS game compatibility. Windows XP, released in 2001, was the merger point — the first mainstream consumer release built on the NT kernel rather than DOS, ending the DOS-based Windows line for good. Every Windows version since — XP, Vista, 7, 8, 10, 11 — has been an NT-kernel descendant of the operating system Cutler’s team started building in 1988.
Why this lineage matters
Nearly every “Windows internals” topic worth understanding — the security token and ACL model, the Service Control Manager, the object manager and handle tables — originates from decisions the original NT team made in the late 1980s and early 1990s, explicitly designed to avoid the reliability and security limitations of the DOS-based Windows it eventually replaced entirely. Windows’ current architecture isn’t an accumulation of patches on top of 1985’s Windows 1.0 — it’s the mature descendant of a genuinely separate, from-scratch operating system project, which is exactly why it holds up structurally as well as it does three decades later.
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