- The implications of 2's complement are significant.
- Basically, they imply that a single chip, called Arithmetic Logical Unit, can be used to encapsulate all the basic arithmetic and logical operators performed in hardware.
- It may be instructive to describe the thought process that led to the design of this particular ALU. First, we made a list of all the primitive operations that we wanted our computer to be able to perform. Next, we used backward reasoning to figure out how x, y, and out can be manipulated in binary fashion in order to carry out the desired operations. These processing requirements, along with our objective to keep the ALU logic as simple as possible, have led to the design decision to use six control bits, each associated with a straightforward binary operation. The resulting ALU is simple and elegant. And in the hardware business, simplicity and elegance imply inexpensive and powerful computer systems.
- In any given computer, the overall functionality of the hardware/software platform is delivered jointly by the ALU and the operating system that runs on top of it. Thus, when designing a new computer system, the question of how much functionality the ALU should deliver is essentially a cost/performance issue.