Q. Illustrate benefits of register addressing mode?
The key benefits of register addressing are:
- Register access is faster than memory access and henceforth register addressing results in faster instruction execution. Though register gets operands only from memory so the operands that must be kept in registers are selected efficiently andcarefully. For illustration if an operand is moved in a register and processed only once and then returned to memory then no saving takes place. However if an operand is used repeatedly after bringing into register then we have saved few memory references. So the task of using register efficiently deals with the task of finding what operand values should be kept in registers such that memory references are minimised. Generally this task is done by a compiler of a high level language while translating the program to machine language. Same like thumb rule the frequently used local variables are kept in the registers.
- The size of register address is smaller than the memory address. It reduces the instruction size. For illustration, for a machine having 32 general purpose registers only 5 bits are needed to address a register.
In this addressing scheme effective address is calculated as:
EA = R
D = (EA)