The Raspberry Pi is a complete computer on a circuit board. It's a hobbyists device and has been commonly used to teach people how to program and learn the basics of computer science. The circuit board has one large chip located in the centre with a number of different connectors located around the edges. These connectors allow for a range of hardware to be connected giving it the versatility to be expanded. The below image is of the 256MB model, key components have been highlighted.
