The iPhone and iPod touch have a limited amount of screen real estate. Given their small screen size, when presenting a drill-down interface, we use a UINavigationController to swap between a list of items and a detailed view for an item.

The iPad, on the other hand, has plenty of screen space to present both views using a built-in class called UISplitViewController. UISplitViewController is an iPad-only class that presents two view controllers in a master-detail relationship. The master view controller occupies a small strip on the lefthand side of the screen, and the detail view controller occupies the rest of the screen.