A line printer can move paper in one direction, and then print a line of up to 132 characters. The PDL developed was simple. The first character of each line sent to the printer specified how far to move the paper, and the rest of the line was printed. A space indicated that the line should be printed just after the preceding line. Daisy wheel printers can move the paper up or down and the print head left or right, with great precision.
Some printers can even vary how hard the characters are pressed into the page.
PDLs were introduced which used control characters or escape sequences to control the printer. Each make and model of printer had a custom PDL which corresponded to the exact set of features available for that printer. Prior to introduction of Laser Printers, designing a PDL was straight forward. The hardware of the target printer had a limited set of capabilities, and each capability got a command to control it. The arival of Laser Printers confused the PDL writers.