A computer is a machine that processes data according to instructions. It can perform calculations and make decisions much faster than humans. A computer has four main functions: input, process, output, and store data. It works by accepting input, processing it, producing output, and storing processed data. The typical components of a personal computer are the system unit, display, and external devices like a keyboard, mouse and printer. The system unit contains the central components including the motherboard, CPU, memory and storage devices.