Operating System (OS)
System maintenance:

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

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Operating System (OS)
The instruction register

is a hardware memory device which denotes the location of the current instruction being executed.
contains the address of the memory location that is to be read from or stored into.
None of these
contains a copy of the designated memory location specified by the MAR after a "read" or the new contents of the memory prior to a "write".
is a group of electrical circuits (hardware), that performs the intent of instructions fetched from memory.

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