Microsoft L2 Mobile Mouse 3500 GMF-00273 Cyan Blue USB RF Wireless BlueTrack Mouse Power Supply: 1 AA battery (included) System Requirement: 100 MB HD for Windows 7, Windows Vista, Windows XP (excluding Windows XP 64-bit) OS, 30 MB HD for Mac OS X v10.4x - 10.6x OS, 1 AA battery (included)