Operating System (OS)
The Memory Address Register

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 hardware memory device which denotes the location of the current instruction being executed.
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.