The algebra of self-similarity and its applications

In a magnetic tape unit, guides are mounted on the back plate above the tape buffer vacuum columns. The back plate is offset to form one side of a threading guide which is wider than the guides through which the tape travels during normal operation of the unit. The glass in the vacuum column door of the cabinet forms the outside wall of the threading guides when the door is closed. A tape trough is mounted on the door to provide a path for the tape to travel under the head when the door is closed. The guides, upper air bearings, magnetic read/write head, head and skew block assembly, threading guides, beginning of tape/end of tape (BOT/EOT), low speed area sensor (LSA), high speed rewind foot assembly (HSRW), erase head, and tape cleaner are all mounted on the back plate which can be easily removed from the machine for service, or for changing the components that determine the magnetic tape path. The tapered vacuum columns are asymmetrical, one with respect to the other, to improve tape tension over the head and capstan. The tape cleaner has a blade and a perforated vacuum plate for pulling the magnetic tape into proximity to the blade.