Difference between Register Mode and Register Indirect Mode

Prerequisite – Addressing Modes

1. Register Mode: In register addressing mode, the operand is placed in one of the 8-bit or 16-bit general-purpose registers. The data is in the register that is specified by the instruction.

Example:

MOV R1, R2 

Instruction has register R2 and R2 has operand. 

2. Register Indirect Mode: In register indirect addressing mode, the address of the operand is placed in any one of the registers. The instruction specifies a register that contains the address of the operand. 

Example:

ADD R1, (R2) 

Instruction has register R2 and R2 has the memory address of operand. 

Difference between Register Mode and Register Indirect Mode are as follows:time-consumingregisteredregistered

Parameters	REGISTER MODE	REGISTER INDIRECT MODE
Operand	The operand is placed in the general-purpose register.	The operand’s offset is placed in one of the registers.
Address Field	In register mode, the address field contains the effective address of the operand.	In register indirect mode, the address field contains a reference of the effective address.
Register References	It requires only one register reference to access data.	It requires two register references to access data.
Calculations	No further calculation is required to perform the operation.	Requires further calculation to find the effective address.
Processing Speed	Register addressing mode is fast.	Register indirect addressing mode is slow.
Accessing of data	It is easier to access the data in register mode.	It is a bit complex to access the data in register indirect mode.
Uses	It uses temporary variables.	It uses pointers.
Advantage	Requirement of a small address field and no time consuming memory accesses.	There is no such constraint imposed on the address range by the address field.
Disadvantage	Constrained Address Space	To retrieve the operand, there is need for two memory references for the execution of instruction: one to get its address and another to get its value.

Register mode and Register indirect mode are two addressing modes in computer architecture that are used to access data stored in registers.

In Register mode, the operand of an instruction specifies a register name as the destination or source of the data. For example, the instruction ADD R1, R2, R3 performs an addition operation on the contents of registers R2 and R3, and stores the result in register R1. Register mode is a fast and efficient addressing mode because the data is accessed directly from the register, without needing to fetch it from memory.

On the other hand, in Register indirect mode, the operand of an instruction contains the memory address of a register, instead of the register name itself. The instruction then accesses the data stored at the memory location pointed to by the register. For example, the instruction ADD R1, (R2) performs an addition operation on the contents of the memory location pointed to by register R2, and stores the result in register R1. Register indirect mode is slower than Register mode because it requires an additional memory access to fetch the data.

Here are some key differences between Register mode and Register indirect mode:

1. Operand: In Register mode, the operand specifies a register name as the destination or source of the data, while in Register indirect mode, the operand contains the memory address of a register.
2. Access Time: Register mode is faster than Register indirect mode because the data is accessed directly from the register, while Register indirect mode requires an additional memory access.
3. Memory Use: Register mode does not use memory to access data, while Register indirect mode requires memory to store the address of the register.

Overall, Register mode and Register indirect mode are two different ways of accessing data stored in registers. Register mode is faster and more efficient because it accesses the data directly from the register, while Register indirect mode requires an additional memory access.

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