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 index register, X
- The auxiliary register, B
- The carry bit
- The Interchange Memory and A (IMA) instruction
- The Compare and Skip (CAS) instruction
- Almost all arithmetic instructions
- The sense switches
- Input/Output keys
- The 8-bit character manipulation instructions
- The instructions concerned with double precision operation
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.