 Overstriking can be used to make boldface text by printing the same line twice without advancing the paper.It can also be used to make underlined text by printing a line containing underscore characters in the print positions occupied by the text to be underscored.Mainframe printers originally had a carriage control tape, with 12 channels (1–9, A, B, C) that can be assigned a fixed position on the page by punching a hole, allowing the printer to skip a variable distance down the page to a fixed location.