H-24 serialDrum Nov65

This document is an Instruction Manual for the Digital Equipment Corporation (DEC) Type 24 Serial Drum, published in 1965.

It describes the Type 24 Serial Drum System as an auxiliary data storage device for PDP-1, PDP-4, and PDP-7 programmed data processors. Key aspects include:

• Functionality: It stores and retrieves data in blocks of 256 computer words (sectors), with a memory capacity up to 131,032 18-bit computer words. Data is transferred in parallel from the computer but written/read serially on the drum surface using NRZ phase modulation. It includes core memory address control, track selection, data transfer control, and error checking (parity and data transmission timing errors).
• Operation: Transfers are program-controlled via I/O instructions (DRLCWR for write, DRLCRD for read), initiating data break cycles and automatically incrementing memory and drum addresses.
• Physical Description: The unit is a cabinet (21-5/8" W x 25-3/4" D x 67-7/16" H, weighing 550 lbs) containing the drum mechanism, logic racks, power supply, and control panels.
• Maintenance: The manual details adjustments for timing, sense amplifiers, and drum heads, as well as marginal checks, diagnostics, and head pad replacement procedures.
• Technical Details: It covers drum format (tracks, sectors, word structure), principles of recording and playback, and provides comprehensive engineering drawings and interface information for connecting to PDP computers.