Operating System (OS)
The instruction 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".
contains the address of the memory location that is to be read from or stored into.
None of these
is a group of electrical circuits (hardware), that performs the intent of instructions fetched from memory.

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Operating System (OS)
The term 'polling' in a computer means a process by which a computer system

detects/corrects errors
None of these
inquires to see if a terminal has any transaction to send
multiplexes the inputs and updates the memory accordingly
decides correct alternative by analysing several ones

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