DOSDOS (Disk Operating System) manages IBM-PC-compatible computers and, in its original definition, is responsible for operating the peripheral storage devices such as floppy disks and hard drives. More generally, it is the operating system of a computer and works as the main interface between CPU and peripheral hardware and between CPU and user.
DOS is included in the name of a number of operating systems such as MS- DOS, ISM PC-DOS and Novell's DR-DOS. The term was first used by IBM for the disk operating system of their model 360 in the mid-1960s.
Today, DOS commonly refers to the disk operating system which is found in the majority of PCs, called either MS-DOS or Microsoft Disk Operating System. DOS was a clone of CP/M (Control Program for Microcomputers, an early microcomputer system for 8-bit computers) for IBM-PC computers equipped with the 8088 Intel chip . MS-DOS 1.0 was introduced in August, 1981 simultaneously with these computers. The license for producing IBM's operating system was given to Microsoft's CEO Bill Gates because IBM thought the future was in hardware and not in software production. The Microsoft Corporation also made sure that DOS could be licensed to only PC clone manufacturers by Microsoft. The high unit numbers of DOS sold by Microsoft allowed it to sell its product at a cheap price and soon, despite competition, it was the industry standard. DOS has been able to survive for 14 years, because it's simple and can be extended easily by other programs such as the popular shareware command shell 4DOS.
DOS is a single-user operating system and runs only one program at a time. It is also limited to work with one megabyte of memory, because the 16-bit addressing method with 64kB-word memory segments limits the addressable memory area to 1088kB-words, 640kB conventional memory for application programs. At the time DOS was invented, one megabyte of memory was enough for most applications.
MS-DOS is also the basis of the graphical user interface MS-Windows which overcomes the limitations of DOS by allowing the user to run several MS-DOS programs together with MS-Windows at the same time. MS-DOS comes with more sophisticated utility programs which allow the user to communicate more directly with the CPU. These utilities include programs for copying, deleting, displaying text files and formatting the hard drive, and others.