On Mon, Mar 29, 2021 at 5:16 PM Erik E. Fair <fair-tuhs@netbsd.org> wrote:
Line printers are distinguished not by the width of the paper but by the printer having enough print heads to print an entire line of output at a time. That speed advantage made them the preferred output device for many-page program listings, as opposed to a teleprinter terminals which were more suitable for interactive computing.
There were originally two styles, the drum printers which DEC sold(e.g. LP20)  and the chain printers that IBM offered (e.g. 1401).  The drum had all the characters in each of the 132 columns (the upper case only printers were faster because the alphabet was on the drum in two places).  The IBM ones has slugs on a rapidly spinning chain that was horizontal (and parallel) to the line being printed.    The chain was easily replaceable by the operator - which was one of the duties we would have.  When a user queued a printer a set of symbols (i.e. the chain of the needed output characters) was specified and the system queued it until the printer had been properly provisioned.   For instance, CMU printed checks with a special chain and film ink, so once a night the operator would configure the printer, and tell the queue to print them).  Some chains were faster than others, the standard one had N copies of each character.

In common to both schemes is that each both styles had 132 hammers and when the proper character was in the position needed, the hammer fired to make an impression the ribbon on the paper, which was caused the noise people associated with computer printers.  The high-end IBM 1401 had a hydraulic cover that came down over it and was controlled by the channel processor (it would auto-open when it needed to be serviced - like a new box of paper).

This led to the "first commandment of fancy printers": Thou shalt not leave thine coffee on top of the printer. -- jpl