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  This service is provided only in the PC/XT fixed-disk ROM BIOS. This
  service commands the XT's fixed-disk controller to format a track in which
  the disk media is defective. The disk controller records which sectors are
  defective in a table located in a reserved cylinder. The register
  parameters are the same as those shown in Figure 10-3, except that
  register AL contains a sector interleave value and no address need be
  specified in ES:BX.