Bidirectional Retrieval of Magnetically Recorded Data

This document describes a data storage system using a magnetic tape medium, specifically designed for efficient bidirectional data retrieval. The system utilizes a specialized mark track, separate from the data tracks, which records binary control words. These control words identify data blocks and frames, and are formatted such that they are decoded into identical control signals regardless of whether the tape is moving in the forward or reverse direction. The system uses Manchester polarity-sensed recording, allowing the decoder to interpret data and control markers accurately in either direction, which simplifies the logic required for data processing and improves operating reliability and speed. The patent includes detailed descriptions of the mark track format, the timing track used for synchronization, the decoding logic, and the interaction with the tape controller.