The IBM SELECTRIC Composer: Memory Backspace

This paper describes the design of the memory backspace system as it now appears in the IBM SELECTRIC Composer. The memory backspace system employs a sensing pawl mechanism in conjunction with the escapement pinwheel and the unit backspace mechanism to provide character-by-character backspace capability. By sensing set pins on the pinwheel, the mechanism “remembers” the location of previously typed characters and permits the carrier to be returned precisely to any print position within the memory “length” without operator measurement or visual alignment.