2. The official name of PC-DOS.
3. (disk operating system) The original DOS (trademark) written by IBM for the series-700 computers was one of the first major operating systems to be offered by a mainframe manufacturer. It was introduced shortly after IBM’s still more primitive system, OS. DOS gave users the ability to construct files on disks that held images of punched cards and that could serve as the input to programs; similarly output ultimately destined for printers was spooled into temporary disk files. The user was responsible for much of the management of these files, and had to contend with details of their physical location on disk and with their creation and disposal.