NO. 4 ESS: mass announcement subsystem

This paper describes a new hardware subsystem developed to provide mass announcement capabilities for No. 4 ESS. The subsystem records, stores, and plays back recorded announcements for distribution through the No. 4 ESS switching network. Announcements are stored in digital form on a moving-head disk system. Microprocessors are used for control of disks and of interfaces. Duplicated hardware ensures high reliability, and extensive self-testing capability is provided