A system bus is a single computer bus that connects the major components of a computer system,combining the functions of a data bus to carry information, an address bus to determine where it should be sent or read from, and a control bus to determine its operation. The technique was developed to reduce costs and improve modularity, and although popular in the 1970s and 1980s, more modern computers use a variety of separate buses adapted to more specific needs.
The system level bus (as distinct from a CPU's internal datapath busses) connects the CPU to memory and I/O devices.Typically a system level bus is designed for use as a backplane.