Abstract: A serial impact printer and including a single cam member for properly establishing and maintaining the throat gap distance between a character imprinting surface and the platen at a print point and for raising and lowering a selected ribbon, of a composite marking correcting ribbon pack assembly, to and from the print point. A short throat gap distance is needed for commercially acceptable printing speeds in this hammer mass printer, and is needed for high quality printing; conversely, a long throat gap distance is needed for print point visibility at all other times. The cam member has plural camming surfaces which coordinate ribbon position with throat gap distance.

Abstract: A recording disk cartridge comprises a housing in which at least one recording disk may be mounted for rotation about its axis. The housing has a peripheral side wall about which a ridge is formed, the ridge being defined by a plurality of sections at least some of which are spaced from one another in a direction parallel to the axis of rotation of a disk mounted in the housing. The dimensions and spacings of the ridge sections are such that the contour of the peripheral side wall at the lower surface of the ridge is the substantial complement of the contour of the peripheral side wall at the upper surface of the ridge. The cartridge also comprises a cover including a peripheral side wall having a contour at its upper surface substantially the same as that of the peripheral side wall of the housing at the lower and upper surfaces of the ridge.