HP EY703AA. Movement detection technology: Optical, Device interface: PS/2, Movement resolution: 400 DPI, Buttons quantity: 2, Scroll type: Wheel. Power source: Cable. Product colour: BlackMost compelling reasons are, PS/2 more secure than USB, optical better than mechanical for tracking, easy use plus easy cleaning. Customers are migrating now making PS/2 the preferred standard over the 2 button scroll.