Mac OS X 10.3.5 Panther gives you everything you need to live in the digital age. The entire system and its applications are designed to work well with each other and suit your individual computing style. Mac OS X features a stunning user interface called Aqua, making work and play on the Mac even more intuitive for new users, while providing powerful, customizable tools for professionals. At the foundation of Mac OS X lies an industrial-strength UNIX-based core operating system that delivers unprecedented stability and performance. Part Number M9227LL/A.