Computer Systems 5 1.1. Personal Computer System The conventional desktop system comprises a main unit, separate keyboard and mouse, and monitor. The main unit has connectors for these (when wireless peripherals are not available) and universal serial bus (USB) ports for memory sticks, printers, scanners, etc., as well as hardwired (Ethernet), or wireless (Wi-Fi) network interfaces. The circuit board (motherboard) in the main unit carries a group of chips which work together to provide digital processing of information and control of input and output devices. A power supply for the motherboard and the peripheral devices is included in the main unit. The laptop has the same components in a compact form, with integrated keyboard and screen, while tablet computers are even more compact with a touch-sensitive screen and no keyboard. The difference between a microprocessor and microcontroller system is illustrated quite well by comparing a desktop computer with a touch-screen game console or mobile phone. The facilities and applications are similar, they just differ in scale and complexity. A block diagram (Figure 1.2a) is a good way to show such a system in simplified form, so we can identify the main components and how they connect. In the case of the disk drives and