Operating System (OS)
You should choose sleep option when

You are leaving for a very short time and want to resume you work shortly
The computer is tired after working for the whole day
You finish working and going to bed
When computer gets hanged frequently. Let it sleep for some time

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

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