Comfort meets control! All-day comfort and scrolling come together in the Kensington Orbit(TM) Trackball with Scroll Ring. Kensington has been a world leader in trackball innovation, and this model is part of that heritage. The scroll ring allows you to fly through web pages and documents. And all while delivering comfort and space savings no mouse can match. Ambidextrous for either left or right handed users. Compatible with Windows XP, Windows Vista, Mac OS X