SERIAL DRUMS 250/251 INSTRUCTION MANUAL VOLUME 1

This manual provides operating and maintenance instructions for the Digital Equipment Corporation Serial Drums Type 250 and 251, which serve as auxiliary data storage devices for PDP-5 and PDP-8 computers, respectively.

The document covers the following key areas:

• Functional and Physical Description: Details the drum system’s operation, including data storage, transfer timing, and the physical cabinet specifications.
• Principles of Operation: Explains the NRZ (non-return-to-zero) phase modulation recording technique, drum formatting, and the block diagram of internal components such as the Drum Core Location Counter, Drum Control, and Sense Amplifiers.
• Interface and Programming: Provides tables of input/output signals and defines the IOT instruction codes used to control the drum systems.
• Installation and Maintenance: Details site requirements, preventive maintenance schedules (including mechanical checks and marginal checks), and corrective maintenance procedures such as head pad replacement and system troubleshooting.