54 mm
                    __   ____________
                (4)/o/==/          //\
               (e)/o/  /          //  ;
              (a)/o/  /  __      //  /
                / /  /  (__)    //  /
               / /  /          //  /
           (a)/o/  /  __      //  /
          (3)/o/  /  (__)    //  / 73 mm
         (2)/o/  /          //  /
        (1)/o/  /          //  /
          /_/  /__________//  /
 10.5 mm  \ \==\__________\\ /
           \____________\\__;  ( view from beneath )
DAT Cassette

The redundant terms "DAT tape" and "DAT cassette" are used to address the media itself apart from the format specification that it was designed for { see DAT }. At the above dimensions of 73 X 54 X 10.4 mm, the DAT cassette is slightly larger than half the size of a traditional analog cassette. The design was developed and standardized for the DAT format, and is such that it physically protects the fragile tape inside. This tape is of 3.81 mm width { often erroneously referred to as 4 mm tape }. Upon insertion into a DAT deck, the following takes place: (a) a slider protecting the tape hubs is retracted to reveal them, (b) the cassette lid is opened to allow access to the 3.81 mm tape { often referred to as 4 mm tape }, (c) tape guides draw the tape from the cassette and wrap the tape around a rotary drum. To keep tape slackness at a minimum, a hub brake mechanism has been implemented within the cassette. Each cassette also features the holes indicated in the ASCII diagram above.

Those which are numbered are recognition holes, and are used so that the deck can identify the type of cassette inserted into it. The first three form a code with four defined states. Given holes 1, 2, and 3, the codes are as follows: 000 { standard pitch, 13-µm tape }, 010 { standard pitch, thin tape }, 001 { wide pitch, 13-µm tape }, 011 { wide pitch, thin tape }, where 1 is open and 0 is closed. Thus, the second hole corresponds with tape thickness, and the third with pitch. The fourth hole (4) identifies a prerecorded {1}, or nonprerecorded tape {0} tape. DAT cassettes also feature a safety tab to stave off accidental recording or erasure. It can be slid toward the center of the cassette, causing a copy prohibition hole (e) to open {1} on the underside shown above. The other holes marked with (a) are datum holes, and are used for alignment purposes. A notch on top of the cassette is used as a loading grip.

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