What Is DOS (Disk Operating System)? - TechTarget

More history and future of DOS

The arrival of the microprocessor in the 1970s started a computing revolution, and the market for personal computers (PCs) began to boom. IBM released the IBM 5150 Personal Computer in August 1981. To speed up the development of this new computer, IBM decided to license various components from other companies.

IBM's first choice for an OS was the CP/M-86 software from Digital Research, but disagreements over nondisclosure agreements and licensing led IBM to choose a CP/M-like OS from Microsoft that was originally called QDOS 86-DOS.

Microsoft bought the rights to market QDOS 86-DOS in 1980. This OS was created by Tim Paterson at Seattle Computer Products (SCP) and was originally called QDOS, an acronym of Quick and Dirty OS. The number "86" refers to the fact that the OS was originally designed to be used with the Intel 8086 processor. After leaving SCP for Microsoft in 1981, Paterson worked on the PC-DOS version of 86-DOS for IBM's PC. PC-DOS was the first widely installed DOS used in PCs running on Intel 8086.

Microsoft produced its own almost identical version of PC-DOS called MS-DOS, which was first released in 1981. As PC sales grew, the ubiquity of MS-DOS grew as well. Subsequent versions of the OS provided improved performance and included additional functionalities, such as support for foreign and extended characters and larger HDDs. Later versions of MS-DOS also enhanced memory management, featured an improved text editor, and provided network support.

When Microsoft first introduced Windows as a GUI for MS-DOS, early users had to type "WIN" at the DOS prompt to launch the Windows program. Windows has since evolved from being a GUI program running under MS-DOS to a full OS taking over as the default OS, though it was not until Windows XP that consumer versions of Windows stopped relying on the DOS program win.com to bootstrap the Windows kernel.

The last retail version of MS-DOS was MS-DOS 6.22; PC-DOS 2000 was the last retail release of PC-DOS. MS-DOS was still bundled as part of Windows but no longer required a separate software license. It can still be run under Windows using a command processor that emulates the MS-DOS interface. There is also an open source version of DOS called FreeDOS that is based on and compatible with MS-DOS. Other versions of these OSes include DR-DOS, ROM-DOS and PTS-DOS (PhysTechSoft DOS).

Because of the many legacy applications that they support, disk operating systems will likely continue to be used for the foreseeable future. Today, they can be used for simple embedded systems or other use cases because they provide machine independence and because the licensing costs are zero for free or open source OSes.

That said, these legacy OSes present critical security problems that make it hard to safeguard them against modern cyberattacks such as SQL injections, man-in-the-middle (MitM) attacks, zero-day vulnerabilities, and more familiar attacks from viruses, worms, ransomware and Trojans.

Disk operating systems played a significant role in the early development of personal computing. Today, some 55 years after their initial development, they hold a place as one of the most important types of OSes in the history of computing.

The latest Microsoft OS is Windows 11. Check out this Windows 11 crash course for desktop admins and Microsoft users, and explore what you need to know when planning to upgrade to Windows 11.

Note: For disk operating system, the acronym used is always DOS (all three letters in uppercase). The acronym DoS with a lowercase "o" is short for denial of service, a method of attacking a networked computer by sending it an abnormally high number of requests in order to exhaust its resources so that genuine users cannot gain access.