A computer system can be thought of as a series of components connected together using one or more buses. The bus carries electronic data between the many components, each component acting as an information source and information receiver.
The system unit is responsible for ordering, sequencing, and executing all operations necessary for proper system operation. For example, it collects data from other components within the computer including clock signals that regulate various functions by telling them when to take place; monitors what’s happening in memory so software has access to this information; talks with other devices on external communication channels, such as USB ports or keyboards; talks with other computers on communication networks like Ethernet cables.