1. A data reader arranged to read a data-holding medium containing data comprising both user and non-user data, set data being held in at least one set, and each said set being arranged into datasets, said non-user data holding information relating to said user data and being interspersed therewith, said data reader comprising at least one read head arranged to read said data-holding medium and generate a data signal comprising user data and non-user data, said non-user data being arranged to identify said user data within said sets, processing circuitry being arranged to receive and process said data signal and obtain said user data from said data signal using said non-user data to identify said user data within said data signal.