DOS meaning in Information Technology ?

A disk operating system (abbreviated DOS) is a computer operating system that resides on and can use a disk storage device, such as a floppy disk, hard disk drive, or optical disc. A disk operating system must provide a file system for organizing, reading, and writing files on the storage disk. Strictly speaking, this definition does not apply to current generations of operating systems, such as versions of Microsoft Windows in use, and is more appropriately used only for older generations of operating systems.

Disk operating systems were available for mainframes, minicomputers, microprocessors and home computers and were usually loaded from the disks themselves as part of the boot process.