Parallel Drum

The Type 23 Parallel Drum is an auxiliary data storage device designed to augment the main core memory of the PDP-1D computing system. It features 32 fields, each capable of storing 4096 18-bit words with an odd parity bit. The manual provides a comprehensive functional and physical description of the system, including:

• Principles of Operation: Details on return-to-bias recording, timing chain generation, and the function of control elements like the Drum Counter (DC), Initial Location Register (IL), Word Counter (WC), and Drum Core Location Counter (DCL).
• Interface and Programming: Specifications for signal levels and the IOT instructions (DIA, DWC, DCL, DBA, DRA) used for system communication.
• Installation and Maintenance: Site requirements, equipment turn-on/turn-off procedures, and extensive maintenance guidelines including preventive, corrective, and circuit-level troubleshooting.
• Appendices: Includes the diagnostic program (DEC-1-137-M) and detailed engineering drawings of the system modules and wiring.