This document provides an overview of the key components inside a computer system unit, including the motherboard, processor, memory, ports, expansion slots, and power supply. It discusses the functions of these components and how they work together to process data. The document also describes different types of processors, memory, ports, and expansion cards that can be used to enhance system capabilities. Mobile computers and tablets are discussed, along with guidelines for selecting processor and memory configurations based on intended usage. Basic cleaning and maintenance of the system unit is also covered.