Operating System (OS)
System maintenance:

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

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Operating System (OS)
The Memory Address Register

is a hardware memory device which denotes the location of the current instruction being executed.
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.
None of these
contains the address of the memory location that is to be read from or stored into.

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