Concept
A disk operating system (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 provides a for organizing, reading, and writing on the storage disk, and a means for loading and running programs stored on that disk. Strictly, this definition does not include any other functionality, so it does not apply to more complex OSes, such as Microsoft Windows, and is more appropriately used only for older generations of operating systems. Disk operating systems for mainframes, minicomputers, microprocessors, and home computers are usually loaded from the disks as part of the boot process. Early computers predate disk drives, floppy disks, or modern flash storage. Early storage devices such as delay lines, core memories, punched cards, punched tape, magnetic tape, and magnetic drums were used instead. Early microcomputers and home computers used paper tape, audio cassette tape (such as Kansas City standard), or no permanent storage at all. Without permanent storage, program and data entry is done at front panel switches directly into memory or through a computer terminal or keyboard, sometimes controlled by a BASIC interpreter in ROM. When power is turned off, any information is lost. In the early 1960s, as disk drives became larger and more affordable, various mainframe and minicomputer vendors introduced disk operating systems and modified existing operating systems to use disks. Hard disks and floppy disk drives require software to manage rapid access to block storage of sequential and other data. For most microcomputers, a disk drive of any kind was an optional peripheral. Systems could be used with a tape drive or booted without a storage device at all. The disk operating system component of the operating system was only needed when a disk drive was used. By the time IBM announced the System/360 mainframes, the concept of a disk operating system was well established.