The document describes the main components of a computer system. It discusses the motherboard, which is the main circuit board that contains sockets for additional boards. It also outlines the power supply unit, which supplies power to the computer and regulates voltage. Hard disk drives are described as the primary storage device that holds data permanently when installed internally. Other components mentioned include the optical disc drive, RAM, CPU, cooling fan and heatsink for the processor, IDE and SATA cables to connect hard drives, video and network cards, and sound cards.