Computer architectures describe how a computer's hardware components are connected, as well as the data transmission and processing methods used. Different computer architecture configurations have been designed to improve data processing by speeding up data movement. The CPU is at the middle of the basic architecture, with main memory and an input/output system on each side The central input/output controller is a second device configuration . The main memory is the place in the computer system from which all data and instructions flow in and out in a third computer architecture. A fourth computer architecture connects all devices in a computer system with a common data and control bus . The dual bus architecture is an improvement over the single shared central bus architecture. To improve overall performance, this architecture either separates data and control over the two buses or shares them.