DOS (Disk Operating System)
DOS (Disk Operating System)
When most people hear DOS, they probably think of MS-DOS. And that is understandable, because Microsoft’s DOS became the dominant operating system for the IBM PC and the huge number of compatible machines that followed.
But MS-DOS wasn't the only DOS in town.
There was actually a whole family of DOS operating systems, some sharing ancestry, some developed independently, and some created specifically to be compatible with MS-DOS. They could look remarkably similar from the command prompt, but behind that familiar C:\> there were some interesting differences.
Where it all started
The story begins with 86-DOS, developed by Seattle Computer Products around 1980–81. Tim Paterson wrote it for SCP's 8086-based computers, and it caught Microsoft's attention when IBM was looking for an operating system for its new PC.
Microsoft licensed 86-DOS, developed it further, and turned it into MS-DOS.
IBM licensed Microsoft's DOS for the IBM PC and sold it as PC DOS.
So the basic family tree looks like this:
86-DOS
│
└── Microsoft
│
├── MS-DOS
│
└── IBM PC DOS
For quite a few years, MS-DOS and PC DOS were extremely close relatives. If you sat down at an IBM PC running PC DOS, you would have found the environment very familiar to anyone who had used MS-DOS.
Eventually, however, Microsoft and IBM went their separate ways. IBM continued developing PC DOS while Microsoft increasingly concentrated on Windows, with DOS eventually becoming something that lived underneath Windows rather than being the operating system you bought and booted into.
MS-DOS
MS-DOS became the DOS that most people encountered during the 1980s and early 1990s.
It grew considerably from its relatively humble beginnings. Later versions added support for hard disks, subdirectories, device drivers, memory management, disk compression and a growing collection of utilities.
There were also plenty of DOS versions that were essentially Microsoft's DOS with an OEM's name attached. Compaq, Zenith and other manufacturers supplied their own versions, sometimes with their own additions.
MS-DOS 6.22, released in 1994, was the last major standalone version sold by Microsoft. DOS didn't actually disappear at that point, though. It continued underneath Windows 95, Windows 98 and Windows Me in various forms.
For many people, that was the beginning of the end of DOS as an operating system you deliberately booted into.
PC DOS
PC DOS was IBM's version of DOS.
IBM had licensed Microsoft's DOS for the original IBM PC, and for many years the two products remained extremely similar. Eventually IBM developed its own features and utilities, and PC DOS became increasingly distinct from MS-DOS.
IBM continued the PC DOS line well after Microsoft had shifted its attention towards Windows, eventually producing versions such as PC DOS 7 and PC DOS 2000.
So although MS-DOS and PC DOS started life as very close relatives, by the later years they were following rather different paths.
DR-DOS — the alternative
Microsoft wasn't the only company interested in DOS.
Digital Research, the company behind CP/M, developed DR-DOS as an MS-DOS-compatible operating system. It wasn't simply Microsoft's DOS with a different name; Digital Research built its own implementation while aiming to provide compatibility with existing DOS software.
DR-DOS became particularly interesting because it often offered features and improvements that Microsoft users had to wait for, especially around memory management.
The name changed several times over the years.
Digital Research's DOS became Novell DOS after Novell acquired Digital Research. Later, following further changes of ownership, it became Caldera DR-DOS and subsequently DeviceLogics DR-DOS.
The name may have changed, but the basic idea remained the same: provide a DOS-compatible environment without being Microsoft's DOS.
And there were others
DR-DOS wasn't the only alternative.
ROM-DOS, developed by Datalight, was designed primarily for embedded systems. Rather than expecting a traditional hard disk and desktop PC, it could run from ROM or flash storage and was used in specialised equipment where a small DOS-compatible environment was useful.
There was also PTS-DOS, developed in Russia, along with several much less well-known DOS-compatible systems such as RxDOS and REAL/32.
These systems didn't necessarily compete with MS-DOS on the desktop. Some occupied very specific niches where DOS compatibility was useful but Microsoft's full operating system wasn't required.
FreeDOS
Then there is FreeDOS, which is probably the best-known modern DOS project.
FreeDOS began in 1994 as an open-source attempt to provide a free and legally independent DOS-compatible operating system. It wasn't created from Microsoft's source code; instead, the developers implemented their own DOS environment and utilities.
And remarkably, it is still being maintained.
FreeDOS is useful today for exactly the sort of things you might expect: running old DOS software, supporting legacy hardware, experimenting with vintage computing and simply having a proper DOS environment available without needing an original Microsoft DOS disk.
It is also a nice reminder that DOS never quite died.
DOS today
DOS is obviously no longer competing with Windows or Linux for the desktop. That particular battle ended a very long time ago.
But DOS continues to survive in some rather unexpected places.
Embedded equipment, industrial systems, legacy machines, retro-computing projects and enthusiasts all provide reasons for keeping DOS-compatible systems alive. FreeDOS remains the most visible modern example, while other specialised DOS implementations continue to exist for particular purposes.
So when we talk about "DOS", we're really talking about a family rather than a single operating system.
There was 86-DOS, which started the story; MS-DOS and PC DOS, which became the dominant versions; DR-DOS, which provided a serious alternative; and a collection of other systems that kept the DOS idea alive in specialised applications.
And somewhere along the way, that little C:\> prompt became one of the most recognisable sights in personal computing.
FreeDOS
FreeDOS is an open source DOS-compatible operating system. Any program that works on MS-DOS should also run on FreeDOS.
FreeDOS is the only (I believe) actively developed DOS.
DOS Programs
4DOS
Synopsis: 4dos is a command.com replacement for MS-DOS and Windows. A very useful tool released in 1989 which has a large number of enhancements over the default command.com
Website: 4dos.info