An ultrasound system which performs two dimensional imaging is upgradeable to a system which also performs three dimensional ultrasonic imaging. The ultrasound system contains space in which an optional 3D beamformer may be installed to provide the ultrasound system with three dimensional imaging capability. When the 3D beamformer is installed a scanhead select module connects one of a plurality of scanhead connectors to the proper beamformer for the imaging procedure commanded by the user.