Abstract: Apparatus and a method for controlling the reading and writing operation of a peripheral storage system such that a magnetic recording medium, having small defective areas in the magnetic surface at which data cannot be reliably recorded may be used. Each data track on the magnetic recording medium has a reserve capacity which is used as a special gap. The recording medium is initialized such that the distance from a point of origin to a surface defect in each track is recorded in a header area in each track. The apparatus and method herein described cooperate with this initialized magnetic recording medium so as to control the format of data recorded onto the magnetic recording medium such that any defect in the recording medium will not affect a reading or writing operation of the storage system.