Abstract: An erasure preventing thumbwheel is located in the front wall of a cartridge and is rotatable in an opening in the front wall. The thumbwheel has a larger diameter central portion which is exposed through the opening and includes a flat section which corresponds in size and shape to the opening. When the flat section registers with the opening, the tape is write-protected. The thumbwheel has a circumferential ridged gripping portion at one edge of the central portion which extends around the non-flat cylindrical section of the thumbwheel. The gripping portion does not extend along the edge of the flat section.

Abstract: A control system adapted to control a plurality of transformer relays. An electrical isolation network is coupled to each of a plurality of transformer relays, having a pair of common control lines and providing electrical isolation for each of the plurality of transformer relays. A switch is coupled to the electrical isolation network and is coupled in parallel to the plurality of transformer relays providing selection of state of all of the plurality of transformer relays. The electrical isolation network may also provide control, as e.g. unidirectional current flow, for selecting a state of each of the plurality of transformer relays. In a preferred embodiment the electrical isolation network includes an array of diodes.