Mainframe printing uses some very simple control characters 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, followed by a second overstruck line of text.

Mainframe printers also have 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 a special position.

ASA carriage control characters are still used in printer output from mainframe applications and software today, and is not limited to seasoned software or applications dating from the days of the line printer. ASA carriage control characters are interpreted by other software before being printed on modern computer printers.

Example output containing ASA carriage control characters:

This is the first line on the page
This is the third line on the page
This is the 6th line on the page
 This is the 7th line on the page
____    the                      - Overstrike the 7th line 

Example as printed output:

This is the first line on the page
 
This is the third line on the page
 
 
This is the 6th line on the page
This is the 7th line on the page - Overstrike the 7th line

External links

• More elaborate description at Felgall Mainframe
• IBM Printing Reference for AIX compilers

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