F-03 555-550 brochure 196403

This document describes the Digital Equipment Corporation (DEC) Microtape system, presented as a "significant new concept in magnetic tape systems" offering a fast, reliable, and low-cost input/output and updating solution.

The system comprises two main components:

1. Microtape Type 555 Dual Tape Transport:

   • Handles 3.5-inch reels of 3/4-inch Mylar tape (260 feet, equivalent to 3 million bits or 4,000 feet of paper tape).
   • Records at 375 bits per track inch at 80 inches per second, achieving an effective transfer rate of 90,000 bits per second.
   • Features bi-directional operation, fixed-position addressing for selective updating of individual words or blocks, and a simple transport mechanism that reduces wear.

2. Microtape Control Type 550:

   • Manages up to four 555 transports (8 drives) and interfaces with DEC PDP-1 and PDP-4 computers.
   • Utilizes automatic Mark track decoding and program interrupt facilities for efficient data transfer, allowing the main program to continue computation during tape operations.

Key features highlighted:

• Redundant, Phase Recording: Ensures transfer reliability and reduces skew/drop-outs.
• Pre-recorded Timing and Mark Tracks: Simplify programming by providing block and word addressability.
• Modes of Operation: Includes Search, Read, Write, and Move, with program interrupt logic for efficient data handling and error detection.

The document also details available programs for both PDP-1 and PDP-4, including:

• Basic Subroutines: For searching, reading, and writing data.
• MICROTOG: A collection of maintenance and diagnostic routines.
• MICROTRIEVE: A utility for easy data storage and retrieval via the computer console.

Specifications include a capacity of 577 256-word blocks per reel (3 x 10^6 bits) and a transfer rate of 15 KC characters, with 256-word blocks read or written in 53 milliseconds (forward direction). Access times range from a typical 5 seconds to a worst-case 40 seconds.