Pre-block ID mark for multi-directional block location when using a unidirectional coding format

摘要

An asynchronous method for locating individual blocks of data in a tape drive, without having to read the blocks of data is provided. The invention comprises placing an ID mark adjacent to the data blocks and inter-block gaps on the tape. The ID mark contains a small amount of information about the next respective data block on the tape. The ID mark is encoded such that the same detection mechanism that detects the inter-block gap can also retrieve the ID mark information, without having to process the entire block of data associated with a particular ID mark. The ID mark is symmetrical such that it can be detected and decoded in the forward and backward direction, allowing the tape drive to find a desired block of data by searching either forward or backward, even when the magnetic tape uses a unidirectional data format.