The PS Vita does not use UMDs. Instead, it uses cartridges and digital downloads. The UMD is going extinct, putting current PSP owners in a bind should they want to play their PSP titles on the Vita.
Sony’s next generation handheld will, as previously promised, support downloadable PSP titles. The PlayStation Vita will even let you take advantage of its dual analogue sticks to control some software. But what about those of us with nothing but PSP games on UMD?