Data are transferred to and from the disk in blocks, accordingly data are stored in block-size regions known as sectors. To avoid imposing unreasonable precision requirements the adjacent sectors are separated by intra?track(record) gaps.
In order to identify positions within a track there are must be starting points on the tracks and ways for identification the start and the end of each sector. These requirements are handled by means of control data recorded on the disk. Thus, the disk is formatted with some extra data used only by the disk driver, and they are not accessible to the user.
In Fig. Winchester Disk Track Format each track contains 30 fixed-length sectors of 600 bytes each. Every sector holds 512 bytes data, plus control information useful to the disk controller.
The ID field is a unique identifier or address used to locate a particular sector.
The SYNCH byte is special bit pattern that determines the beginning of the field.
The track number identifies a head, since this disk has multiple surfaces.
The ID and data fields contain an error-detecting code (CRC).