Before Windows Was NT: How Microsoft Built a Non-Unix World (And Why It Still Matters)

When people talk about operating systems today, the conversation almost always bends toward Unix-like systems. Linux, BSD, macOS POSIX everywhere.

But the personal computer world did not grow up on Unix.

It grew up on something very different.
Messier.
Less elegant.
More practical.

It grew up on DOS → Windows → NT.

To understand why Windows NT exists and why it still dominates PCs you need to understand what came before it.

1. The World Before NT: DOS Was Never Meant to Rule PCs

Before Windows had a kernel, it had a shell.
And before the shell, it had MS-DOS.

MS-DOS was not designed as a “real OS”.

It was:
• single-user
• single-tasking
• no permissions
• no memory protection
• no multitasking
• no security model

Just:
CPU → RAM → program → hardware.

That was enough in the early 1980s.

PCs were:
• standalone
• offline
• used by one person
• rebooted daily
• trusted by default

Security didn’t matter because nothing was connected.

DOS wasn’t elegant it was fast and cheap.

And cheap won.

1. Early Windows Was Not an Operating System

This part shocks people.

Windows 1.0 → Windows 3.11 were not operating systems.

They were graphical environments running on top of DOS.

DOS did the real work:
• disk access
• memory
• hardware
• program loading

Windows just drew windows.

That’s why:
• one crashed app could freeze the entire system
• “Ctrl+Alt+Del” became survival instinct
• blue screens were normal
• multitasking was cooperative (apps had to behave)

This wasn’t bad engineering.
It was a compromise.

Microsoft optimized for:
• cheap hardware
• compatibility
• mass adoption
• software availability

Unix optimized for multi-user systems.
Windows optimized for home PCs.

1. File Systems Before NT: FAT Everywhere

Before NTFS, Windows lived on FAT.

FAT (File Allocation Table)

Used by:
• MS-DOS
• Windows 3.x
• Windows 95/98/ME

Characteristics:
• no permissions
• no users
• no journaling
• simple structure
• easy to corrupt
• easy to recover
• incredibly compatible

FAT survived because:
• it was simple
• it worked on floppies
• BIOS understood it
• every OS could read it

Even today, USB drives and SD cards still use FAT variants.

FAT wasn’t safe but it was universal.

1. The Breaking Point: Windows 95–ME Era Chaos

By the mid-1990s, PCs had changed.

They were:
• always on
• networked
• used for work
• running multiple apps
• handling real data

DOS-based Windows could not keep up.

Problems piled up:
• memory corruption
• system-wide crashes
• no user separation
• malware paradise
• driver instability
• hardware conflicts

Microsoft knew DOS-Windows was finished.

They needed a real operating system.

1. Enter Windows NT: A Clean Break

Windows NT was not an evolution.

It was a reset.

Built by Microsoft engineers (many with VMS background), NT was designed to be:
• multi-user
• preemptive multitasking
• secure
• portable
• hardware-abstracted
• enterprise-grade

This was not Unix.

It didn’t copy fork().
It didn’t copy POSIX semantics.
It didn’t copy Unix philosophy.

It created its own model.

1. NT Architecture (Why It’s Different)

Windows NT uses a hybrid kernel design:
• Kernel (low-level scheduling, interrupts)
• Executive (memory, I/O, security)
• Hardware Abstraction Layer (HAL)
• User-mode subsystems

Everything is an object:
• files
• processes
• threads
• devices
• registry keys

Access is controlled via Access Control Lists (ACLs), not Unix permission bits.

This made NT:
• extremely flexible
• very complex
• painful to document
• powerful for enterprises

1. NTFS: The File System That Changed Windows Forever

NT needed a serious file system.

That became NTFS.

NTFS Features:
• per-file permissions
• journaling
• access control lists
• encryption (EFS)
• compression
• alternate data streams
• large file support
• crash recovery

This was a huge leap from FAT.

NTFS turned Windows into a real multi-user OS.

Even today, NTFS remains one of the most advanced general-purpose file systems in consumer OSs.

1. Why Windows Stayed Non-POSIX (On Purpose)

Microsoft did experiment with POSIX layers.

But they never made POSIX the core.

Why?

Because Windows had to support:
• decades of software
• binary compatibility
• enterprise APIs
• proprietary drivers
• GUI-first applications

POSIX compatibility would have broken everything.

So Windows chose:
compatibility over purity.

And that decision paid off.

1. Other Non-Unix, Non-POSIX PC Operating Systems

Windows wasn’t alone.

Here are other important non-Unix PC OSs, and why they mattered.

Classic Mac OS (Pre-OS X)
• Cooperative multitasking
• No memory protection
• GUI-first design
• Human-centric UX
• HFS / HFS+ file systems

It failed technically but defined modern UI design.

Apple eventually abandoned it because it couldn’t scale.

OS/2 (IBM + Microsoft)
• True multitasking
• Memory protection
• Advanced filesystem (HPFS)
• Way ahead of Windows 95

It failed because:
• IBM moved too slowly
• hardware support lagged
• software ecosystem died

Technically superior.
Commercially doomed.

AmigaOS
• Preemptive multitasking in the 1980s
• Multimedia-first
• Custom hardware integration

It died because:
• bad business decisions
• hardware cost
• market timing

But technically?
Years ahead.

BeOS
• Designed for multimedia
• Multi-threaded by default
• Fast filesystem (BFS)
• Clean, modern design

It lost to Microsoft politics, not engineering.

1. Why Non-POSIX OSs Still Matter

POSIX is not “better”.
It’s just one design choice.

Non-POSIX OSs survive because:
• they solve different problems
• they prioritize compatibility
• they serve real businesses
• they handle legacy
• they focus on users, not elegance

The PC world was never Unix-first.

It was pragmatic-first.

Final Thought

Windows NT exists because DOS was never enough.

It carries:
• the mess of history
• the weight of compatibility
• the needs of enterprises
• the expectations of billions of users

It isn’t beautiful.

But it works.

And in the real world, working beats perfect.