Method and apparatus for controlling motion of storage media

Apparatus for controlling relative rotation of a data storage medium on which data is stored and a rotatable transducer for reading data from said storage medium, said data being stored in data groups comprising tracks extending across said storage medium and the apparatus comprising:

• means for identifying from said data groups a start reread data group at which a data reread process is to start following detection of a data read error condition in a preceding data read process;
• means for reading a track reference value difference stored in at least one track of at least one data group from which data is to be reread during said data reread process;
• means for determining a reread track reference value for use in controlling said relative rotation during said data reread process using said data track reference value difference and a track reference value used in controlling said relative rotation during the preceding data read process;
• and
• control means for using said reread track reference value in controlling said relative rotation during said data reread process.

A method of storing data for use in controlling motion of a data storage medium relative to a rotatable transducer, the data being stored in data groups comprising tracks extending across the data storage medium and the method-comprising:

• determining a previously written date group after which at least one new data group is to be appended or written over existing data stored on the data storage medium;
• obtaining a track reference value for said previously written data group;
• determining a track reference value difference value based on said track reference value for said previously written data group and a track reference value for said at least one new data group;
• and
• storing said track reference value difference value in at least one track of said at least one new data group.

Apparatus for storing data on a data storage medium, the data being stored in data groups comprising tracks extending across the storage medium and said apparatus comprising:

• data assembly means for assembling said data into at least one new data group to be written onto said storage medium;
• appendancy determining means for determining whether said at least one new data group is to be written over existing data or appended to existing data stored on the storage medium and determining a previously written data group after which the at least one new data group is to be written;
• means for obtaining a track reference value for the previously written data group;
• means for determining a track reference value difference value based on said reference value for the previously written data group and a track reference value for the at least one new data group;
• means for incorporating said data track reference value difference value in at least one track of the at least one new data group;
• and
• means for writing said at least one new data group on said storage medium.