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

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