Just as early PDP-11 models had no hardware multiplication support, division routines also had to be provided in software.

Like many other computers of the time, the base PDP-11/20 model has not have a "multiply" instruction. Any program that needs to multiply numbers needs to provide a routine that can use the existing instructions to perform the multiplication operation. One technique is to use a series of shifts and adds, similar to the way multiplication is done by hand.