Operating System (OS)
System maintenance:

is necessary on all systems, regardless of how good
None of these
is not required if the system is well written
is usually not necessary
always requires several programs

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Operating System (OS)
Most of the microcomputer's operating systems like Apple DOS, MS DOS and PC DOS etc. are called disk operating systems because

they are memory resident
they are initially stored on disk
they are partly in primary memory and partly on disk
None of these
they are available on magnetic tapes

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