Operating System (OS)
System maintenance:

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

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Operating System (OS)
The Register - to - Register (RR) instructions

None of these
which perform an operation on a register operand and an operand which is located in the main store, generally leaving the result in the register, except in the case of store operation when it is also
All of these
have both their operands in the main store.
which perform indicated operations on two fast registers of the machine and leave the result in one of the registers.

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