Microtape

This document describes the Digital Equipment Corporation (DEC) Microtape system, specifically the Type 550 Microtape Control and the Type 555 Dual Microtape Transport. Introduced in 1963, the system was designed to provide the storage capacity and speed of magnetic tape while maintaining the convenience of paper tape.

Key features of the Microtape system detailed in the document include:

• Recording Technique: Uses Manchester-type polarity-sensing, which offers high reliability by making the system insensitive to signal amplitude variations and allows for the modification of individual bits.
• Data Reliability: Employs redundant tracks and physical head arrangement to mitigate issues like tape skew and crosstalk.
• Functionality: Supports bi-directional reading and writing, individually addressable blocks and words, and variable block formats. It utilizes a pre-recorded timing and mark track to provide synchronization, error checking, and addressability.
• Operation: The system operates in several modes (Search, Read, Write, and Move) controlled by specific programmed subroutines. These allow for flexible data management, including program storage, multi-user random access, and continuous data logging.
• Software Support: The document outlines the provided subroutines (basic search/read/write, MICROTOG for maintenance, and MICROTRIEVE for library management) for the PDP-1 and PDP-4 computers.
• Technical Specifications: Detailed appendices provide instruction lists, operation charts for different modes, and hardware specifications (e.g., 260-foot reels, 90,000 bits per second transfer rate, and specific power and dimension requirements).

The document concludes by noting the potential for future expansion, such as file protection and compatibility across different computer models.