SDAT
SDAT (or S-DAT) is a format of Digital Audio Tape developed by Sony. The "S" prefix denotes that it is the format which uses a stationary magnetic head. Shinji Ikari is seen throughout the Neon Genesis Evangelion TV Series and Movies listening to an SDAT player, noteably switching between tracks 25 and 26. Some fans have postulated that there is a possible connection between tracks 25 and 26 and the last 2 episodes of the TV Series.
The SDAT in Rebuild
In Evangelion 2.0: You Can (Not) Advance, Shinji mentions that his SDAT player was given to him by his father, Gendo Ikari. Also in 2.0, the SDAT skips from track 25 to 27 shortly before the plot diverges from that of the original series, lending credence to the theory that the track numbers are related to the episodes.
