Method for extraction of a variable length record from fixed length

Abstract

A method enables a host processor, which employs variable length (VL) records, to communicate with disk storage which employs fixed length (FL) sectors for storage of the VL records. The method comprises the steps of: a) deriving a first control data structure for an update VL record, the first control data structure including information describing segments of the update VL record; b) determining a disk track that includes a FL sector wherein am old VL record commences that corresponds to the update VL record; c) reading each FL sector in the disk track and creating a control data structure which includes information describing each VL record stored in the disk track; d) substituting in a control data structure for the old VL record that corresponds to the update VL record, information regarding update data from the first control data structure; e) recording in the disk track, data indicated by each control data structure determined in steps c) and d); and f) if the old VL record ends at other than a sector break of a FL sector, reblocking VL records into FL sectors which are recorded thereafter on the disk track. The invention also enables a read action to be accomplished in one rotation of a disk even though it commences at a FL sector that is not at the beginning of a VL record to be accessed.