This machine was introduced in 1966. The DDP-516 and the later H316, which has an identical instruction set, form the core of the Series-16. The DDP-116 is clearly the forerunner of these machines, but seems to have had a limited impact commercially. The DDP-416 appears to be a development that is off the main path for the Series 16. The H716 seems to have come too late to be commercially successful.