Being one of the few mechanical components in a typical computer system, hard drives consume a significant amount of the overall power used by a computer. Spinning down a hard drive reduces its power consumption, but only works when no disk accesses occur, limiting overall effectiveness. We have designed and implemented a technique to extend disk spin-down times using a small non-volatile storage cache called NVCache, which contains a combination of caching techniques to service reads and writes while the hard disk is in low-power mode. We show that combining NVCache with an adaptive disk spin-down algorithm, a hard disk?s power consumption can be reduced by up to 90%.