The document discusses the functional units of a computer system. It describes the five main components: the input unit, central processing unit (CPU), memory unit, arithmetic & logical unit, and output unit. The CPU contains the arithmetic logic unit, memory unit, and control unit. The control unit manages data transfer between units and obtains instructions from memory. The arithmetic logic unit performs arithmetic and logic operations. The memory unit temporarily stores running programs and data. The input unit allows data entry, while the output unit receives data from the CPU and translates it into audio, visual or printed output. All units communicate via a common bus system.