ALU operations use register operands only. Usually 3 operands, all in registers. On many machines, accesses to objects larger than a byte must be aligned. Misalignment complicates the hardware. Addressing Modes An addressing mode can specify a constant, a register or a location in memory.
Operand is in a register.
Operand is a constant encoded directly in the instruction. Similar to displacement except the constant is 0. Two registers are added together to get the memory address. The memory address is contained directly in the instruction. Also, it contains an explicit constant.