This document provides an overview of the key components inside a computer's system unit, including the motherboard, processor, memory, expansion slots, ports, and buses. It describes the basic functions of the processor's control unit and arithmetic logic unit. It explains how data is represented digitally using bits and bytes. It differentiates between types of memory, such as RAM, ROM, and cache. It outlines various expansion slots and adapter cards that can enhance the system unit's functions. It defines ports and connectors and lists common types including USB, FireWire, and serial ports.