Most of the microcomputer’s operating systems like Apple DOS, MS DOS and PC DOS etc. are called disk operating systems because A. they are memory resident B. they are initially stored on disk C. they are available on magnetic tapes D. they are partly in primary memory and partly on disk E. None of the above

The correct answer is: B. they are initially stored on disk.

Disk operating systems (DOS) are a type of operating system that is stored on a disk and loaded into memory when the computer is turned on. This allows the computer to access files and programs that are

stored on the disk, without having to load them into memory all at once. This makes DOS systems more efficient than earlier operating systems, which were stored in memory and required all programs to be loaded into memory before they could be used.

A. They are memory resident. This is not the case for DOS systems, which are stored on disk and loaded into memory when the computer is turned on.

C. They are available on magnetic tapes. This is not the case for DOS systems, which are stored on disk.

D. They are partly in primary memory and partly on disk. This is not the case for DOS systems, which are stored on disk and loaded into memory when the computer is turned on.

E. None of the above. This is the correct answer.