history, what is it and what is it for

The DOS system It was one of the most widespread in the past, a key part of the IBM PC, as can be seen in history. However, little by little it has been replaced by other more modern operating systems. What not too many people know is that there is still a DOS that has survived and is usually installed on some current laptops, or that there are still some machines that still maintain MS-DOS.

A unknown to many new generationsand even with some gaps for users of previous generations, who believe that the origin of everything was Gates and Microsoft…

What is TWO?

DOS system logo

A DOS system (Disk Operating System), as its name suggests, is a type of operating system that resides on a disk, being able to use a storage medium from it, such as another floppy disk drive, a hard disk, etc. This system is very simple compared to the current ones, but its code is enough to perform the basic operations expected from an OS:

  • Provide an FS to read and write data to
  • Manage hardware resources through the kernel and drivers
  • Resource management and main memory
  • Serve as interface between user and machine

This type of system was very popular in the past, especially on IBM PCs, where MS-DOS from Microsoft It was one of the most widely used operating systems of the time and the predecessor of the current Microsoft Windows, although the Windows NT kernels were not derived directly from MS-DOS as non-NT Windows did.

Windows 1.0 was nothing more than MS-DOS with a graphical interface, as were versions 2.0, 3.x, Windows 95 (4.0), Windows 98 (4.1), and Windows Me (4.9). After that, a Windows NT era would begin, with NT 3.1, NT 4.0, Windows 2000 (5.0), XP, Vista, 7, 8.x, Windows 10, and Windows 11.

Microsoft tried to fix all the problems its systems based on the DOS-kernel for current computing, including security for the Internet age. To do this, it would start the creation of a new portable kernel, compatible with OS/2 and POSIX, with multiprocessing support and with improvements for the Internet age.

This project was going to name OS/2 3.0, as Microsoft was working with IBM at the time to develop the OS/2 operating system. However, with the success of Windows 3.0 at the time, Microsoft decided to bet on a Windows API and not OS/2, something that would cause tension between IBM and Microsoft. At that time, IBM continues to develop OS/2 and Microsoft would focus on its project, renaming OS/2 3.0 as Windows NT, which would be the replacement for DOS.

Then Microsoft would hire a team of developers from DEC (Digital Equipment Corporation), including Dave Cutler, to build NT with Dave’s experience who had worked on VMS and other operating systems. The rest to this day you already know…

History of the DOS system

DOS system

Although many relate TWO With MS-DOS, the operating system of this Microsoft family, the truth is that the start of this system is not linked to the Redmond company. Everything goes back to the era of the IBM PC, when the blue giant presented its new concept with an Intel 8088 microprocessor. This computer needed an operating system.

Therefore, the IBM company tried to find a supplier and initially thought of CP/M, an operating system developed by Digital Research and that at that time it had the vast majority of compatible software. In this way, CP/M-86 should be born, compatible with the Intel 8088. But the negotiations turned out to be a failure, since Digital did not want the payment system imposed by IBM, but wanted to continue with its method of collecting royalties.

In addition, Digital Research threatened IBM with a lawsuit for infringing intellectual property, and for this the blue company had to offer CP/M-86 with their PCs to resolve this conflict, even though the operating system was released several months after the machine itself. In this way, the user could choose the operating system to use.

After Digital, IBM thought of using QDOS, which was similar to CP/M-80, and whose company had been created in Seattle. The problem with this system was that it had been designed to run on its own hardware, not the IBM PC. For this reason IBM and Microsoft began negotiations to port QDOS to the IBM PC hardware. Microsoft basically adapted QDOS and gave it to IBM as PC-DOS.

Bill Gates would approach Seattle Computer Productsthe developer of QDOS (86-DOS), and Microsoft bought the system for reportedly $50,000.

CP/M-86s sold poorly due to its high price compared to PC-DOS. This generated another dispute between Digital Research and IBM, since the former accused the latter of offering marginal prices to harm its business. All caused by the refusal of Digital to the single payment, while Microsoft had accepted said deal.

Quickly PC-DOS begins to be the new standard of the IBM PC industry. And Digital Research Inc. loses ground with its customers.

Gordon Letwin wrote in 1995 that “DOS was, when we first wrote it, a throwaway product designed to keep IBM happy so they would buy our languages.”

Gordon Letwin of Microsoft, 1995

… and then “the coconut” arrived. When AT&T began selling UNIX, Microsoft and IBM saw it as a big threat, so they started developing a replacement for DOS called OS/2. But it would be of little use, since UNIX began to become popular in universities and companies, being one of the best operating systems in history.

Little by little UNIX would also evolve with some forks and Unix-like systems like Linux. But TWO didn’t quite die, a remnant remained beyond the first versions of Windows. Jim Hall would publish a manifest to create an open source DOS replacement. He would be joined by other developers such as Tim Norman and Pat Villani.

These developers would initiate the project to create a open source DOS kernel, a COMMAND.COM shell, and some basic utilities. The result was a distribution called FreeDOS that would be released in September 2006, and available under the GNU GPL license. It may be used, copied, or modified royalty-free and legally.

Family TWO


The DOS system family it’s huge, and it goes way beyond Microsoft’s MS-DOS. You can find many related systems such as:

  • 86-DOS or QDOS: QDOS stands for Quick and Dirty Operating System. It was written by Tim Paterson for 16-bit 8086 chips. It was based on Gary Kildall’s CP/M. This system would later be purchased by Bill Gates for Microsoft and serve as the basis for his PC-DOS and MS-DOS.
  • PC-DOS: This other DOS system was created by Microsoft from the previous one to work on IBM PCs with Intel 8088 chips.
  • MS-DOS: is a variant of the previous one, with some differences. It is developed by Microsoft, but while PC DOS was intended for the original IBM PCs, Microsoft sold MS-DOS only to clones that appeared on the market.
  • DR-DOS: is an MS-DOS compatible operating system for the IBM PC. Digital Research Inc. (DRI), specifically Gary Kildall, was its developer. It derives from PC DOS 6.0, which itself was an advanced successor to the CP/M-86. As a result of the changes in ownership, it would be sold under various names such as Novell DOS, Caldera OpenDOS, etc.
  • FreeDOS: Formerly known as PD-DOS or Free-DOS, it is a free, open-source, x86-compatible operating system in addition to running under virtualization. It can boot from a bootable USB stick and is fully DOS compatible for running legacy software. Although it is released under the GNU GPL, other parts of the project are not licensed under the same license, such as 4DOS (a command line interpreter), which is distributed under the MIT license. On the other hand, the most notable differences as MS-DOS are that it supports Ultra-DMA controller, support for large hard drives, FAT32 support, DOSLFN driver for use of long names in VFAT, and support for modern hardware.

There was other DOS system names in the past, even some that included the denomination in their name, despite not having direct kinship with this family. Some examples are Apple DOS, Atari DOS, Commodore DOS, TRSDOS, AmigaDOS, DOS/360, etc.

Current uses


In 2018, Microsoft made a move that surprised many people, and that is that it released the source code of MS-DOS 1.25 and 2.0 in a GitHub repository. Many wondered what the point of that is if it is no longer used, and many others thought it was a move simply so other people could study the code.

But you should know that MS-DOS is still used currently on some x86 embedded systems where memory and other hardware requirements are minimal. And some in systems that you could not even imagine. The news that the Pentagon is still using Windows 95 and 98 operating systems is not an isolated case.

Many machines still rely on systems that were developed decades ago. Many others also depend on old hardware. Some systems used by NASA continued to use Z80 chip, that’s why they came to buy devices with these chips to try to have spare parts. Or you also have the case of McLaren F1, which needs a Compaq LTE 5280 (a laptop from the 90’s) to upgrade.

But the closest and most well-known case is that of laptops or branded equipment without another operating system, they are only sold with FreeDOS. Instead of opting for a pre-installed Windows operating system, they save on licenses by using this free and open source version of DOS to give their computers an operating system with which to do essential tasks.

Obviously, the ultimate goal of FreeDOS is not to serve as end operating system, but to have a basic system while the user installs the one he has chosen (Windows, FreeBSD, Linux, Solaris,…). In this way, the manufacturer of the OEM equipment does not condition you to pay a license and use a specific system, but you can choose on your own.

Besides, the essence TWO He is still in many other projects. For example in some emulators for retro video games, in emulation software like DOSBox, and more.

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