Difference between Implied addressing mode and Immediate addressing mode
Last Updated : 11 Sep, 2024
In computer architecture the addressing modes play a vital role in defining how the operands of the instructions are to be retrieved. The two are addressing modes that are often employed are the Implied and Immediate addressing modes. Though both play major roles in instruction execution they work differently based on how operands are either specified or deduced. These differences are useful to know in order to write better code that will have a higher efficiency.
What is Implied Addressing Mode?
In implied addressing mode, the operands are specified implicitly in the definition of the instruction. All the instructions which reference registers that use an accumulator are implied mode instructions. Zero address instructions in a stack-organized computer are also implied mode instructions. Thus, it is also known as stack addressing mode.
Advantages of Implied Addressing Mode
- Advantages it in that it simplifies given instructions because the operand is not included.
- Delivery of faster results because the execution of the instruction does not involve an extra memory reference to acquire the operand.
Disadvantages of Implied Addressing Mode
- Relatively rigid as the operand cannot be changed other than in the physical sense by the programmer.
- Appropriate only for particular codes to be executed where the operand is suggested by the operation.
What is Immediate Addressing Mode?
In Immediate addressing mode, the operand is specified in the instruction itself. In this mode, the operand field contains the actual operand to be used in conjunction with the operation specified in the instruction.
Advantages of Immediate Addressing Mode
- Since operand is easily accessible from the instruction then it executes fast.
- It helps to free the machine from the necessity of obtaining operands from the memory.
Disadvantages of Immediate Addressing Mode
- Restricted to minute operand specifications since the operand must fit in instruction area.
- Inapplicable to the operands performant for static data as the operand is encoded in the instruction.
| S. No. | Implied Addressing Mode | Immediate Addressing Mode |
|---|
| 1. | In Implied addressing mode, no operand is specified in the instruction . | In Immediate addressing mode, operand is specified in the instruction itself . |
| 2. | Basically, the operands are specified implicitly in the definition of instruction . | Here, the operands are contained in an operand field rather than address field . |
| 3. | This type of mode can be used in all register reference instructions . | This type of mode is quite useful for initializing the registers to a constant value . |
| 4. | It requires 8 bits or 16 bits long data and is the part of instruction. | It requires more bits than the address. |
| 5. | There is no need to acquire a operand . | It is fast in acquiring an operand . |
| 6. | Zero-address instructions in a stack-organized computer are implied-mode instructions . | The address field of an instruction may specify either a memory word or a processor register. |
| 7. | Example: CMA (Complement Accumulator) | Example: MVI A 45 |
| Feature | Implied Addressing | Immediate Addressing
|
| Addressing method | Implicit: the operand's location is determined by the instruction opcode | Explicit: the operand value is directly specified in the instruction
|
| Operand size | Typically 8-bit or 16-bit | Typically 8-bit or 16-bit, but can also be 32-bit |
| Flexibility | Less flexible: only works with predefined memory locations or registers | Less flexible: only allows for immediate values as operands |
| Code size | Requires less code: operand location is determined by the instruction opcode, which is shorter | Requires more code: additional instructions are needed to load the immediate operand into a register |
| Execution speed | Faster: operand location is determined directly from the instruction opcode | Slower: additional instructions are needed to load the immediate operand into a register |
| Memory usage | Does not use additional memory | Uses additional memory to store immediate values |
| Complexity | Less complex: requires fewer instructions and is generally easier to use and debug | More complex: requires additional instructions and memory accesses, and can be more difficult to debug
|
Conclusion
Both Implied and Immediate addressing modes are used differently in computer architecture though they have their own benefits. Implied addressing is beneficial when the operand is known and while the speed of the instruction execution is of essence. On the other hand, Immediate addressing mode is most useful where the operand wants to be specified in the instruction but, though more versatile than the previous addressing modes discussed here, it has a restriction on the size of the operand. Depending on the circumstances programmers can then select the right mode depending with their ability and efficiency.