The Register – to – Register (RR) instructions A. have both their operands in the main store. B. 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 C. which perform indicated operations on two fast registers of the machine and leave the result in one of the registers. D. all of the above E. None of the above

The correct answer is: C.

Register-to-register (RR) instructions are instructions that perform an operation on two registers and leave the result in one of the registers. For example, the instruction ADD R1, R2, R3 adds the contents of register R2 to the contents of register R1 and stores the result in register R3.

The other options are incorrect. Option A is incorrect because RR instructions do not have both their operands in the main store. Option B is incorrect because RR instructions do not perform an operation on a register operand and an operand which is located in the main store. Option D is incorrect because not all RR instructions leave the result in the register. For example, the instruction MOV R1, R2 copies the contents of register R2 to register R1. In this case, the result is left in register R2.

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