What are the function of the central processing unit?

Answer 1

There are 3 different types of registers:

1. Those involved in program sequencing, e.g. the "PC" register.

2. Those involved in address calculation of variable - "SP" and "B".

3. Those involved in arithmetic and logic operations, like "A" and "X"

Then there are some special registers and "flags".

The (1) is used by the instruction unit to identify and request the next instruction to load. The next instruction can be calculated based on a comparison "IF A > B JMP to End otherwise execute next."

The registers that is used in arithmetic and logical operations are kept in the CPU to make this run faster. There is no memory access needed to add the content of 2 register, making this a much faster operation than adding memory. So, other computers than the Intel designed, use more registers and can benefit from this.

The CPU will require 2 registers to be able to feed the two arguments to the ALU for evaluation, and obtain the result in one of the registers.