Abstract: A relatively simple and easily installed transfer unit is disclosed employing a movable cartridge bin assembly which travels horizontally between two or more cabinets of respective tape cartridge library systems, to enable the expansion of individual library systems thereby increasing overall mass storage system capacity. The bin assembly is presented to a typical cartridge handling robot of respective library systems as if it were part of the stationary bin array housed within the cabinet, which allows the cartridge to be accessed and loaded in a constant orientation. A drive means provides the translation of the bin assembly and cartridge, and depots at preset stop locations include sensor means for indicating the location of the bin assembly and the presence of a cartridge in the bin assembly.

Abstract: A digital servo track pattern for a magnetic medium which can be recorded and reproduced by a recording and reproducing system. The servo track pattern has a plurality of digital mark patterns recorded thereon, each of said digital mark patterns having a leading identifier field of digital bits, a trailing identifier field of digital bits and a field of digital synchronizing data located between said leading and trailing identifier fields. The leading identifier field of digital bits is electrically equivalent during reproducing while the medium is moving in a first direction to the trailing identifier field of digital bits while the medium is moving in a direction opposite to said first direction.