What DOS was: the operating system the first computers stood on

Before computers were controlled by windows, icons and a mouse, a black monitor with a blinking cursor reigned, where you typed commands. That was DOS, the operating system the first personal computers grew up on. Let us recall what DOS was, how it worked and why its mark lives on today.

What DOS was

DOS (Disk Operating System) was an operating system controlled by text commands that became widespread in the 1980s and early 1990s. The best-known version was MS-DOS from Microsoft. Instead of clicking a mouse, you gave the computer instructions by typing a command and pressing Enter.

It was the foundation the first personal computers ran on, and even the first versions of Windows were originally a layer on top of DOS.

How it worked

• A text, not graphical environment. No windows or icons, just the command line.
• One task at a time. DOS ran one program until it finished. No switching between multiple windows.
• Working through commands. You controlled everything by typing, which required knowing commands by heart.
• Modest requirements. It ran on hardware that is unimaginably weak today.

Typical commands

Anyone who experienced DOS remembers commands like:

• dir to show the contents of a folder.
• cd to change folders.
• copy to copy files.
• del to delete.
• format to format a disk.

These commands may remind you of something, and not by chance. They live on in today’s Windows command line and in a similar form also in Linux commands.

Why it mattered

DOS was the springboard of a whole era of personal computers. It taught a generation to work with a computer, laid the foundation for Windows and its logic of control through commands survives in modern systems. Without DOS, today’s computers would look different.

Historical curiosities

Several stories surround the birth of DOS that rank among the best known in the history of computing:

• DOS began as a “quick stand-in”. In 1980 programmer Tim Paterson wrote a system called 86-DOS, nicknamed QDOS, the Quick and Dirty Operating System. Microsoft bought it for roughly 75,000 dollars and licensed it to IBM. Today the purchase ranks among the best bargains in history.
• IBM knocked elsewhere first. It originally wanted the CP/M system from Digital Research for its computer. The deal fell through, however, so IBM turned to Microsoft. Had those negotiations gone differently, software history would look completely different today.
• File names had only 8 + 3 characters. DOS allowed a name of at most eight characters plus a three-character extension, which is why files were called things like REPORT01.TXT. Long names arrived only with Windows 95.
• The notorious 640 KB limit. Programs had only 640 KB of conventional memory available, and working around that limit was daily gymnastics for users and programmers for years.

DOS milestones at a glance

Common myths about DOS

• “DOS was the first operating system.” It was not. Systems for mainframes existed before it, as did CP/M for the first personal computers. DOS was, however, the first mass-market system for the IBM PC and its clones.
• “Bill Gates wrote MS-DOS.” He did not. The original code was created by Tim Paterson; Microsoft bought the system, adapted it and developed it further. The business move, though, was Gates’s.
• “Windows 95 abolished DOS.” In reality Windows 95, 98 and Me still stood on DOS, they just hid it under a graphical environment. DOS disappeared for good only with the Windows NT family, from which today’s Windows descends.
• “DOS is dead.” As a main system yes, but FreeDOS is still used today for firmware updates, in industrial equipment and among enthusiasts.

The legacy of DOS today

As a main system DOS no longer runs, it was replaced by graphical systems like Windows, Linux and macOS. But its legacy is everywhere:

• The command line in Windows is a direct descendant of the DOS idea and many commands still work the same today.
• The drive letters C:, D: and so on come from the times when A: and B: belonged to floppies.
• The FAT file system that DOS used lives on today in USB sticks and memory cards.
• Batch files (.bat) for automating tasks still work in Windows today.
• Retro enthusiasts run old DOS games via emulators, more in the article on retro gaming and emulators.
• Some specific and industrial systems still use the simplicity of text control today.

Conclusion

DOS was a text operating system the first personal computers stood on. It was controlled by commands, did one thing at a time and required knowing commands by heart. Although it was replaced by graphical systems, its legacy lives on in the command line and in the logic of how computers still work under the hood.

This article is part of our Software and system overview.