Disk operating system

A disk operating system (abbreviated DOS) is a computer operating system that 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, microprocessors and home computers and were usually loaded from the disks themselves as part of the boot process.

In the early days of computers, there were no disk drives, floppy disks or modern flash storage devices. Early storage devices such as delay lines, punched cards, paper tape, magnetic tape, and magnetic drums were used instead. And in the early days of microcomputers and home computers, paper tape or audio cassette tape (see Kansas City standard) or nothing were used instead. In the latter case, program and data entry was done at front panel switches directly into memory or through a computer terminal / keyboard, sometimes controlled by a read-only memory (ROM) BASIC interpreter; when power was turned off after running the program, the information so entered vanished.

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