Operating System (OS)
A critical region is

a program segment where shared resources are accessed
none is the above
a program segment that often causes unexpected system crashes
a program segment that has not been proved bug-free
one which is enclosed by a pair of P and V operations on semaphores

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

None of these
have both their operands in the main store.
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
which perform indicated operations on two fast registers of the machine and leave the result in one of the registers.
All of these

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