Abstract: A high degree of flexibility and speed in dot matrix printing are achieved by providing printing cartridge modules that are so thin, a number can be stacked together and run simultaneously. Depending on the array used, several lines can be printed at the same time, or a single line can be developed from a standard dot matrix character into a fully formed character. In one embodiment, the print wires are formed into a linear array parallel to the flat side of the cartridge module, and the modules are stacked vertically with respect to the print medium. This embodiment is preferred for overlay printing. In a second embodiment, the print wires are formed into a linear array perpendicular to the flat side of the cartridge module, and the modules are stacked horizontally with respect to the print medium. This embodiment is preferred for multiple line printing, and has the additional advantage of being sufficiently flat to fit within the upper and lower planes of a ribbon cartridge.