Like many digital audio players, iPods can serve as external data storage devices when connected to a computer. Discontinued versions include two generations of the full-sized iPod, all of which had monochrome screens (except for the iPod shuffle) and provide a simple user interface. The hardware of a computer is infrequently changed, in comparison with software and data, which are "soft" in the sense that they are readily created, modified or erased on the computer. The iPod is currently the world's best-selling digital audio player, and its worldwide mainstream adoption makes it one of the most popular