The Raspberry Pi Camera Module is a custom designed add-on board for Raspberry Pi. It attaches to Raspberry Pi by CSI interface, which was designed especially for interfacing to cameras.
The board is around 25mm x 20mm x 9mm. It prefect for mobile or other applications where size and weight are important. It connects to Raspberry Pi by a short ribbon cable. The camera is connected to the BCM2835 processor on the Pi via the CSI bus, a high bandwidth link which carries pixel data from the camera module to the processor.