The OS Genealogy
Operating systems did not emerge in a vacuum. Every OS you use today is the result of decades of “biological” evolution—ideas were shared, companies were sued, projects were abandoned, and successful kernels were “forked” into new lineages. To understand why Windows uses backslashes \ and Linux uses forward slashes /, or why macOS feels like a Unix system, we must look at the family tree.
The Dawn of Modern OS (1960s)
In the 1960s, computers were massive mainframes. Users didn’t “use” them; they submitted decks of punched cards.
- Multics: A joint project by MIT, Bell Labs, and GE. It was ambitious and aimed to be an interactive utility. It was too complex for its time, but it introduced the concept of a hierarchical file system and security rings.
- UNIX: Frustrated by the complexity of Multics, Ken Thompson and Dennis Ritchie at Bell Labs created a “simpler” version. They punningly called it UNIX (the “Uni” version of “Multi”-cs).
The Great Forking
Unix was written in C, making it portable. Soon, it began to split into two major branches:
- System V (AT&T): The “commercial” Unix.
- BSD (Berkeley Software Distribution): A version created at UC Berkeley that added critical features like the TCP/IP stack (the foundation of the internet).
The Rise of the PC (1980s)
While the giants were fighting over Unix, a small company called Microsoft bought a hobbyist OS called QDOS (Quick and Dirty OS) and turned it into MS-DOS for the IBM PC.
- MS-DOS: A single-user, single-tasking OS. It had no protection and no GUI.
- Windows 1.0 - 3.1: These were not operating systems; they were just GUI “shells” that ran on top of MS-DOS.
The Shift to NT (1990s)
Microsoft realized that the DOS lineage (Win 95/98) was too unstable. They hired Dave Cutler (the architect of VMS) to build a new, modern, secure kernel from scratch: Windows NT (New Technology).
- The Crash of the Lineages: Windows XP was the first consumer version of Windows to abandon the old DOS foundation and use the stable NT kernel. Every Windows version since (7, 10, 11) is a direct descendant of NT.
The Linux Revolution (1991)
In 1991, Linus Torvalds, a Finnish student, was frustrated that he couldn’t afford a expensive Unix workstation. He decided to write his own Unix-like kernel from scratch. He used the “GPL” license, which meant anyone could use and improve it for free.
- GNU + Linux: Linus wrote the kernel, but he needed tools (a compiler, a shell, etc.). He used the tools created by Richard Stallman’s GNU Project. This combination—the Linux kernel and GNU tools—created the OS that now runs the entire world’s servers, supercomputers, and Android phones.
The Resurgence of Apple (2001)
After almost going bankrupt, Apple bought Steve Jobs’ company NeXT. NeXT had built an OS called NeXTSTEP, which was based on the Mach microkernel and BSD Unix.
- XNU: Apple combined these parts to create the Darwin kernel, which became the foundation of macOS and iOS. This is why your Mac terminal uses Unix commands like
lsandgrep—it literally is a Unix system under the hood.
The Modern Landscape
Today, the world is divided into three major architectural camps:
- The NT Camp: Windows (Proprietary, Hybrid kernel).
- The Unix/BSD Camp: macOS, iOS, FreeBSD, NetBSD (Proprietary/Open, Hybrid/Microkernel).
- The Linux Camp: Ubuntu, Fedora, Android, ChromeOS (Open Source, Monolithic kernel).
In the next few modules, we will dive into each of these systems to see what makes them unique and how they actually function “under the hood.”