Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Mainframe printing uses some very simple control characters at the start of each line to control the movement of the paper through a line printer. "ASA" is the abbreviation of the American Standards Association, a former name for the American National Standards Institute (ANSI), which is believed to have sanctioned these control characters. Overstriking can be used to make boldface text by printing the same line again without advancing the paper. It can also be used to make underlined text by printing a line of underscore characters atop the text. Mainframe printers had 12 channels (1 through 9 and A through C) that can be assigned a fixed position on the page, allowing the printer to skip a variable distance down the page to a fixed location. Normally only channel 1 is preassigned, to the top of the page.

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