Abstract: A sector of data to be recorded on a magnetic medium is formatted by dividing the data sector into a plurality of data segments. Recorded with each segment is a time code which is identical for all segments in a given sector. During recordation of the data and time code for each segment, a cyclic redundancy check (CRC) signal is generated and the CRC signal is recorded after the data and the time code. As data in a segment is recorded, it is also temporarily stored. The temporarily stored data is combined according to a prescribed function with data in the succeeding segment and that function is temporarily stored for combination with the data in the next succeeding segment so that after all segments of data have been recorded there is a function that uniquely represents the data in all data segments. The function is recorded as a check segment. On recovery of the data, an error in any given segment can be detected by employment of the CRC signal associated with the segment containing an error.