Data entered at the keyboard of the teletype could be directed to a perforator or punch which punched a pattern of holes across the width of a paper tape to represent the characters typed. The paper tape could be read by a tape reader feeding the computer. Computer output could be similarly punched onto tape and printed off-line.
The first units had five data hole positions plus a sprocket hole (for the driving wheel) across the width of the tape. These used commercial telegraph code (ITA2 also known as Murray), Baudot code or proprietary codes such as Elliott which were more programmer-friendly. Later systems had eight data holes and used ASCII coding.