Q. Explain about data registers?
The data registers are used just for storing intermediate results or data and not for operand address calculation.
Some dedicated address registers are:
Segment Pointer : Employed to point out a segment of memory.
Index Register : These are used for index addressing scheme.
Stack Pointer: Points to top of stack when programmer visible stack addressing is used.
One of fundamental issues with register design is number of general-purpose registers or data and address registers to be provided in a microprocessor. Number of registers also affects instruction design as number of registers concludes the number of bits required in an instruction to specify a register reference. In common it has been found that optimum number of registers in a CPU is in range 16 to 32. In case registers fall below range then more memory reference per instruction on an average will be required as some of intermediate results then have to be stored in memory. Instead if the number of registers goes above 32 then there is no appreciable reduction in memory references. Though in a number of computers hundreds of registers are used. These systems have special features. These are known as Reduced Instruction Set Computers (RISC) and they exhibit this property.