1. Computer Organization (CO) - It illustrates :The dynamic interaction between the components How the hardware components operate How the hardware components are connected together to form computer system.2.Computer Design (CD) - It is about computerimplementation that illustrates: What hardware should be used How should they be connected3.Computer Architecture (CA) - It illustrates : Various functional modules such as processors and memories Structuring all these modules together to form a computer systemInterface between the machine and the software.1.1.1 Components of a Computer System A system could just be a pen which is composed of only *. three or four hardware components or it can be a computer-based system like a pay-roll system that is composed of thousands of hardware and software components plus human users who take decisions based on information from the computer system. A system is a set of components that interact with each other to achieve some predetermined goal. Example: The digestive system (a system) in a human body is made up of large intestine (one component) and small intestine (another component) that work together to achieve proper digestion of food (predetermined goal). Components are also called as sub systems.