I know very little about this machine, which was introduced in April 1967. It seems to have been a cost-reduced DDP-516.

This program shows that, relative to the H316 and DDP-516 machines, the DDP-416 lacked:

The machine had the same cycle time as the DDP-516 (0.96 microseconds). It was intended for control applications that didn't require the more advanced arithmetic.

The standard method to tell the DDP-416 from the DDP-516 is to attempt to set the carry bit (with SCB). This will not be set on the DDP-416.