The format that made the mixtape possible, and made ninety minutes the unit of a friendship. This TDK D-C90 from the early 80s is rebuilt from the cassette standard's drawings and photos of a real one, with a summer 1986 mixtape on it (turn your sound on). Click the cassette to play the side facing you, and again to stop; the clear leader runs for a few seconds before the first song. Your left hub rewinds and your right one fast-forwards, and dragging a hub round winds it by hand, the pencil trick. Turn it over for side B. The songs are the museum's own, and the tape stays where you left it. On a computer, Space plays and stops and the arrow keys wind.