550 prelimManual

This document is a manual for the Microtape system, an input-output device designed for use with PDP-1 and PDP-4 computers.

Key aspects of the Microtape system and the manual's content:

1. System Overview (Section 1):

   • It consists of a Type 550 Microtape Control Unit and a Type 555 Dual Microtape Transport Unit.
   • It aims to combine the flexibility and storage of magnetic tape with the convenience of paper tape.
   • It operates as a program break control, transferring information word-by-word.
   • Applications include data/program storage, editing, on-line system data handling, and continuous data sampling.
   • Specifications include tape speed (80 inches/second), density (375 3-bit characters/inch, 3 million bits per reel), 18-bit word transfer (200 microseconds/word), and bidirectional operation.

2. Operating Instructions & Programming (Section 2):

   • Covers loading the program and transport.
   • Discusses manual switch functions (WRTMR, SELECTOR, WRITE LOCK, FWD-REV).
   • Details preprogrammed subroutines for search, read, write (Microtog for diagnostics, Microtrieve for saving/retrieving data) available for PDP-1 and PDP-4.
   • Provides a Microtape Instruction List for programming, including flags that indicate system status (Data flag, Block end flag, Error flag).

3. Theory of Operation (Section 3):

   • Explains the technical functioning of the control unit, data transfers, and timing/control functions.
   • Details the Manchester recording technique which uses flux changes for bit representation and allows bidirectional reading/writing.
   • Describes the critical role of prerecorded timing and mark tracks for synchronization, block formatting, addressing, and error detection.
   • Explains how the system processes information in different modes: Search, Read, Write, and Move, and how flags are generated and interpreted.

4. Maintenance (Section 5):

   • Outlines preventive maintenance procedures (cleaning, visual inspection, marginal checks) to ensure optimal operation and detect potential component failures.
   • Details corrective maintenance including troubleshooting random information errors, circuit diagnosis, and repair procedures (e.g., soldering, component replacement).
   • Lists test instruments and programs (Rocker, Exerciser, Microtog) used for maintenance.

5. Pertinent Documents (Section 6):

   • Lists related publications (e.g., Digital Modules Catalog, PDP Handbooks) and library programs (e.g., Microtape Control PGM, Microtape Format Pack).
   • Includes a list of engineering drawings for the system.

In essence, the manual provides a comprehensive guide to the Microtape system, covering its design, operational principles, user interaction, programming interface, and maintenance requirements.