MS-DOS - short for Microsoft Disk Operating System - is an operating system commercialized by the Microsoft Corporation. It was the most widely used member of the DOS family of operating systems and was the dominant operating system for the PC compatible platform during the 1980's. MS-DOS was the first true operating system in the computer market.
MS-DOS was originally released in 1981 and had eight major versions released before Microsoft stopped development in 2000. It was the key product in Microsoft's growth from a programming languages company to a diverse software development firm providing the company with essential revenue and marketing resources. It has gradually been replaced on consumer desktop computers by various generations of the Windows operating system.
In the beginning, MS-DOS was developed primarily for IBM machines as their main operating system, however IBM was also working on their own versions of the MS-DOS system. Eventually, they began working together with IBM producing the hardware and Microsoft producing the software.
MS-DOS was not designed to be a multi-user or multi-tasking operating system, however many attempts were made to add these capabilities. The 'Terminate and Stay Resident' (TSR) system calls were originally designed for device drivers and extensible plug-ins that enhance or added features.
Some companies began to tap into the TSR design with products like Side Kick. Add-on environments like Top View and especially DESQview attempted to provide multi-tasking. They did achieve some success when this was later combined with the virtual 8086 mode and virtual memory features of the Intel 80386 chip along with later processors.
MS-DOS was the basis for all of Microsoft's Windows operating systems. However, because of its often difficult command line interface that required user input, Microsoft realized that they needed to come up with a much more user-friendly way to market their operating systems.
Even so, MS-DOS has effectively ceased to exist as a product. It has become the bootstrap loader for Windows 95, Windows 98, and Window ME, but it was integrated as a full product thus ending the days of a standalone disk operating system.
Today, it is still used in various embedded x86 systems due to its simple architecture, minimal memory requirements, and minimal processor speed requirements. The command line interpreter of Windows NT is cmd.exe which maintains most of the same commands and compatibility with DOS.
Without MS-DOS, the operating system we now know today would not be what they are. Even though MS-DOS was a great product at the time, it quickly outlived its usefulness and gave way to the more advanced systems of Windows and their subsequent versions.