250 251 serialDrumVol1 1967

This document is Volume 1 of the "SERIAL DRUMS 250/251 INSTRUCTION MANUAL" published by Digital Equipment Corporation in 1967. It provides comprehensive information for understanding, operating, programming, and maintaining the Type 250 and Type 251 Serial Drum Systems.

The serial drums serve as auxiliary data storage devices designed to augment the main memory of PDP-5 (Type 250) and PDP-8 (Type 251) computers. They store and retrieve data in blocks (sectors) of 128 computer words, transferring 12-bit words (plus a parity bit) in parallel between the computer and the drum, which are then written or read serially on the drum surface using non-return-to-zero (NRZ) phase modulation.

Key areas covered in this manual include:

• Principles of Operation: Detailed explanations of the recording and playback techniques, drum format (tracks, sectors, words), and the functionality of various internal components and control circuits involved in data transfer, addressing, and error checking.
• Physical Description and Specifications: Information on the physical characteristics, dimensions, weight, power requirements, and operational performance specifications of the drum systems.
• Interface: Details on the logic signals and connections between the serial drum and the host computer.
• Installation and Operation: Guidance on site requirements, signal and power connections, and the use of manual controls and indicators for system operation.
• Programming: A list of IOT instruction codes, information on drum format and program timing, and examples of programming subroutines for data transfer.
• Maintenance: Extensive procedures for both preventive maintenance (e.g., mechanical checks, power supply checks, timing adjustments, drum sense amplifier checks, head mounting adjustments, marginal checks) and corrective maintenance (including system and circuit troubleshooting, repair guidelines, and specific instructions for head pad replacement).

The manual emphasizes that it contains proprietary information, intended solely for the proper use and maintenance of DEC equipment. Volume 1 contains the instructional and maintenance text with illustrations and reference data, while Volume 2 contains the engineering drawings.