Microsoft Disk Operating System.

MS-DOS, acronym for Microsoft Disk Operating System. In computer science, MS-DOS—like other operating systems—oversees such operations as disk input and output, video support, keyboard control, and many internal functions related to program execution and file maintenance. MS-DOS is a single-tasking, single-user operating system with a command-line interface.

Operating System (OS), in computer science, the basic software that controls a computer. The operating system has three major functions: It coordinates and manipulates computer hardware, such as computer memory, printers, disks, keyboard, mouse, and monitor; it organizes files on a variety of storage media, such as floppy disk, hard drive, compact disc, digital video disc, and tape; and it manages hardware errors and the loss of data.

In 1996, in response to the increasing relevancy and rapid growth of the Internet, Microsoft renamed its existing MSN service to "MSN Classic" and created a new version, called "MSN 2.0," which combined access to the Internet with web-based multimedia content in a new program known as the "MSN Program Viewer." The service was promoted to existing MSN subscribers beginning October 10, 1996; the general release followed on December 10, 1996.

Microsoft promoted MSN 2.0 with a series of advertisements and promotional materials describing the service with the phrase, "Every new universe begins with a big bang." The company offered the initial release of the new MSN 2.0 service on a CD-ROM that it sent to MSN subscribers in the fall of 1996. When inserted, the CD-ROM opened to the ambitious and flashy MSN Preview, an interactive video-based experience that introduced current and prospective subscribers to the new version of MSN and described the features of the MSN 2.0 software.

The "MSN Preview" was formatted as a guided tour of a mock premiere event for the new MSN. It was hosted by a witty and sarcastic character named "Michael" who welcomed viewers outside of a theatre and then guided them through the theatre to meet several other characters, each of whom represented one of the channels of MSN 2.0's "On Stage" area, which was designed as the main platform for interactive multimedia content in MSN 2.0.

A. 86-DOS (developed at Seattle Computer Products by Tim Paterson for the new Intel 808x CPUs; licensed to Microsoft, became PC DOS/MS-DOS. Also known by its working title QDOS.)
1. PC DOS (IBM's DOS variant, developed jointly with Microsoft, versions 1.0 – 7, 2000)
2. MS-DOS (Microsoft's DOS variant for OEM, developed jointly with IBM, versions 1.x – 6. Microsoft's now abandoned DOS variant)

B. DR-DOS (Digital Research's [later Novell, Caldera, ...] DOS variant)
1. Concurrent DOS (Digital Research's first multiuser DOS variant)
2. Multiuser DOS (Digital Research's [later CCI's. Real's/...] multiuser DOS variant)

C. FreeDOS (open source DOS variant)
D. ProDOS (operating system for the Apple II series computers)
F. PTS-DOS (DOS variant by Russian company Phystechsoft)

G. RDOS (Data General Corp)
1. TurboDOS (Software 2000, Inc.)

H. Multi-tasking user interfaces and environments for DOS
1. DESQview+ QEMM 386 multi-tasking user interface for DOS
2. DESQView/X (X-windowing GUI for DOS)