The PDP-3 is designed to accommodate a variety of input-output
equipment. Standard input-output units include a Paper Tape Reader,
Paper Tape Punch and an Electric Typewriter.
A single instruction, In-Out Transfer (see Central Processor), performs
all in-out operations through the 36 bit In-Out Register. The address
portion of this instruction specifies the in-out function. One bit of
the instruction selects an in-out halt as required.