Technically, the DEC DECwriter series were dot-matrix printers, not line printers. They
differed from their Teletype predecessors only in print-head technology, but both printed
a single character at a time. Daisywheel printers were similar.
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 dot-matrix line printers of the late 1970s made by Printronix, which is
apparently still around.
Erik Fair