In the RR, RX, and RS formats, the contents of the register designated by the R1 field are called the first operand. In the RR format, the R2 field designates the register containing the second operand, and the same register may be designated for the first and second operand. In the RS format, the use of the Rx field depends on the instruction.
The R field designates a general register in the general instructions.
Unless otherwise indicated in the individual instruction description, the register operand is one register in length (32 bits for a general register ), and the second operand is the same length as the first.