TSPS No. 1: Stored Program Control No. 1A Store

Digital storage in the Stored Program Control (SPC) 1A is provided by the piggyback twistor (PBT) memory store. The heart of this system is the P B T module which is composed of pairs of wires wrapped with two magnetic tapes, one piggyback on top of the other. The SPC 1A store has been designed around the P B T memory module. This store meets the SPC 1A requirements of high reliability and low cost with an operating speed that is adequate for the present SPC 1A applications. High reliability is provided by the nondestructive readout (NDRO) characteristic of the P B T memory. The memory element needs no regeneration after reading and is not disturbed by power interruptions. It is alterable at electronic speeds with this feature being protected from accidental use by several independent checks on the write process. Low cost has been achieved by highvolume continuous fabrication of the P B T memory element. The SPC 1A store 1 is used for all the memory needs in the SPC 1A. This is in contrast to No. 1 Electronic Switching System (No. 1 ESS) in which the memory needs were split into two groups, temporary memory for the storage of call-related data and semipermanent 2509