DOS is an acronym for Disk Operating System.
The first personal computers only had 5 1/4 inch floppy drives with a capacity of 512 K or 1 MB. There was an A disk which booted the OS and a B disk which was an application disk for a word processor or spreadsheet application. These were all separate made by different companies. There were no complete office suites back in the day.
Dos was a command line interface so one had to know the commands and their arguments in order to see what files were present or copy a file.
There were several versions of Dos as well from IBM, Microsoft, Corel and others.
Eventually hard drives became available and the first ones had 5 MB and occupied a space of a 5 1/4 floppy drive.
Later versions of Dos had doshell which provided a simple text user interfase and some pulldown menus. This lead to innovations such as Quarterdeck’s Desqview which allowed for simple multitasking in separate sections of the screen, or window.
The Dos Family entry on the jumplist has different shells that were available for Dos.
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