How does the iPod skip protection work?
From the official Apple iPod FAQ: In addition to the hard drive, iPod has a memory cache. It is made up of solid-state memory, meaning that it has no mechanical or moving parts, so it is not affected by movement of the device. iPod skip protection works by preloading up to 25 minutes of music to the cache at a time. iPod plays music from the memory cache rather than the hard drive, so even rigorous activities won’t cause music to skip. This only applies to the full-sized iPod and iPod mini models. The iPod shuffle, iPod nano, and iPod touch models use solid-state flash memory, and consequently, cannot skip.