The Data Doctor is a software diagnostic and repair program supplied by DivaDroid International for in the field maintenance and repair on Deep Space missions or long duration trips.
It does not fully delete the defective files, just overwrites them leaving the damaged data on the hard drive of the mechanoid until the data area on the drive is needed for storage.
The interface is a cross between a school teacher and the stereotype of an old-style computer tech.
The Data Doctor appeared in "Back in the Red: Part Two" in order to reset Kryten back to his factory default settings.
The image of the Data Doctor is based on John Warburton, the template used to create the Series 4000 mechanoid. (RD: Back in the Red II)
Behind the Scenes
The interface was played by Robert Llewellyn, and is considered one of the more notorious elements of Series VIII.