F-03 555-550brochure 6-64

This document describes Microtape, a magnetic tape data storage system developed by Digital Equipment Corporation (DEC) in 1964, presented as a "fast, reliable, low cost in-out facility and updating device."

The system consists of two main components:

1. Microtape Type 555 Dual Tape Transport: This unit features two independent tape drives that handle 3/4-inch Mylar tape on 3.5-inch "pocket-size" reels, each capable of storing up to 3 million bits. It uses a simple, capstan-less drive mechanism, operates bidirectionally at 80 inches per second, and achieves an effective information transfer rate of 90,000 bits per second (transferring 256 18-bit words in 53 milliseconds).
2. Microtape Control Type 550: This control unit can manage up to four dual tape transports (eight drives total). It facilitates binary data transfer between the tape and the computer (PDP-1 and PDP-4 compatible), automatically assembling data into 18-bit computer words.

Key features and advantages of Microtape include:

• Fixed Position Addressing: Allows selective updating of individual words or blocks on tape without disturbing adjacent information.
• Redundant, Phase Recording: Enhances transfer reliability, reduces skew, and minimizes drop-outs due to amplitude variations.
• Pre-recorded Timing and Mark Tracks: Simplify programming by providing timing and addressability for blocks and words, and enable automatic bi-directional compatibility and end-of-tape sensing.
• Bi-directional Operation: Saves time and provides easy access to stored information.
• Compact Design: The transport occupies less than two cubic feet and fits standard rack mounts.

The document also details available programs for the system, including:

• Basic Subroutines: For searching, reading, and writing data.
• MICROTOG: Maintenance and diagnostic routines.
• MICROTRIEVE: A program for easy information storage and retrieval via the computer console.

Overall, Microtape was designed to offer a robust, efficient, and cost-effective solution for data storage, retrieval, and updating in early computer systems.