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

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Operating System (OS)
Semaphores

synchronize critical resources to prevent contention
synchronize critical resources to prevent deadlock
None of these
are used for memory management
are used to do I/O

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