this is the simplest way for an instruction to specify an operand. in this type of addressing the address part of instruction actually contain the operand itself rather than an address of other information -describing where the operand is.
such an operand is called "immediate operand" because it is automatically fetched from the memory and the same time the instruction itself is fetched; hence it is immediately available for use.
- advantages:
- it could use less memory because it does not require an extra memory reference to fetch an operand.
- instruction execution time will be less as instruction itself contains operands.
- disadvantages
- restricting the operand to a number that can fit in an address field.in and instruction will 3 bit address, the operands would be restricted to 3 bits, which limit their usefulness.
- only constant can be supplied this way.
for example IBM 370 has MOVE,COMPARE, BOOLEAN OPERATION as well as sevral other instruction that contain 1 byte immediate operand.
