Explanation:

The acronym 'DOS' stands for 'Disk Operating System'. This term refers to a family of operating systems that were widely used on IBM PC compatible computers in the 1980s and early 1990s. The most famous variant was MS-DOS (Microsoft Disk Operating System). The primary function of DOS was to manage disk storage, files, and provide a command-line interface for users to interact with the computer hardware. Therefore, option (d) Disk Operating System is the correct and universally accepted full form. Options (a) Device Outsourcing System, (b) Device Operating System, and (c) Different Operating System are all incorrect interpretations and do not represent the established meaning of the acronym DOS in the field of computing.