F-15(24) serialDrum Aug63

This document describes the Digital Equipment Corporation (DEC) Type 24 Serial Drum, an auxiliary data storage device designed to augment the main memory of PDP-1 or PDP-4 computing systems.

Key aspects covered:

1. Functionality: The Serial Drum stores and retrieves data in blocks of 256 computer words. Data is transferred in parallel (18 bits) between the computer and the drum, but written and read serially (one bit at a time) on the drum surface, including an added 19th parity bit for error checking. The system includes mechanisms for address control (core memory and drum track), data request and transfer, error detection (parity and timing), and power management.
2. Operation: Transfers are initiated by Input Output Transfer (IOT) pulses. The drum automatically increments core memory and track addresses for sequential block transfers. It supports both read and write cycles, with specific sequences for setting up the transfer, managing data flow through internal buffers (Drum Final Buffer, Drum Serial Buffer), generating/checking parity, and signaling completion or errors to the computer.
3. Physical Description: The device is housed in a standard DEC computer cabinet (21 5/8 inches wide, 25 3/4 inches deep, and 67 7/16 inches high), weighing 500-550 pounds depending on memory capacity (16,384 to 65,536 words). It uses a rotating magnetic drum with heads for data storage, incorporating a fan for cooling.
4. Interface and Controls: It operates on 115V, 60Hz single-phase power, with local or remote (computer-controlled) turn-on options. Logic signals adhere to standard DEC levels. Control switches allow for normal or stop-on-error maintenance modes, and the ability to inhibit writing on specific tracks. Various indicator lamps display the machine's status and register contents.
5. Programming: The document details specific IOT instruction codes (e.g., drlcrd for read, drlcwr for write, drlblk to begin transfer) for the PDP-4 to control data blocks and track addresses. It includes programming examples and explains timing considerations for block transfers.
6. Maintenance: Comprehensive procedures are provided for both preventive (mechanical checks, power supply, timing, head spacing, and marginal checks to identify borderline conditions) and corrective maintenance (troubleshooting, diagnostic programs, signal tracing, aggravation tests for intermittent faults, component repair, and detailed drum head replacement instructions).

The document aims to provide thorough information for installation, operation, programming, and maintenance of the Type 24 Serial Drum, serving as an essential manual for users and technicians.