The Crescendo/NuBus G3 477-500MHz Processor Upgrade for Power Macintosh and Performa from Sonnet is processor upgrade for Power Macintosh and Performa computers. The processor plugs into a NuBus slot on your computer to give it G3 processing power running at 477 to 500MHz depending on the system bus speed. This is a great way to breathe new life into your older Mac computer.