Kensington Orbit USB/PS2 Combo Mouse/Trackball for Windows or USB Mac Mouse/Trackball combo brings together the comfort of a mouse, and benefits of a trackball. Hand-hugging design for natural finger motion, comfortable for right or left-handed users. Natural wrist support eases fatigue Precise trackball cursor control and stationary like trackball, so uses less desk space. Medium-sized ball and two mouse buttons. Mouse/trackball combo has PS/2 and USB connectivity (for PCs and USB Macs) Free downloadable software