DOS stands for Disk Operating System. It was the dominant and standardized operating system for personal computers compatible with the IBM PC architecture during the 1980s and early 90s, with Microsoft's MS-DOS being the most famous version. Unlike modern systems based on windows and mouse input, DOS operated exclusively through a command-line interface, requiring the user to type textual instructions to manage files, format disks, and execute programs. Although it has been replaced by graphical interfaces like Windows, the underlying structure of DOS still underpins many computing concepts, and its command tools remain accessible through the Command Prompt or terminals in current systems.