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BOT marker Short for beginning of tape marker. A physical feature of a magnetic tape by which the tape transport senses on the tape the start of the volume into which data can be recorded, or has been recorded. When the transport senses the marker it commences the logical sequence of recording or reading data. The marker may be, for example, a rectangular strip of reflective material adhering to the tape, a transparent part of the tape, or a hole in the tape, according to the type of tape and transport. The distance of the marker from the physical beginning of the tape allows the tape to be loaded, threaded through the transport, and wound on to a point at which data will be reliably recorded. This distance, and the form of the marker, are defined by the standard pertaining to the type of tape. See also EOT marker. Compare tape mark.