Source : Free On-Line Dictionary of Computing

sector interleave
     
        (Or sector map) The mapping from logical to physical sector
        numbers on a {magnetic disk} designed to optimise sequential
        reads and writes.  Data is usually transferred to and from the
        disk in {block}s or {sector}s where one sector lies within a
        continuous range of rotational angle of the disk.  If logical
        sectors are assigned sequentially to physical sectors
        (0,1,2,...) then by the time one sector has been read and
        processed (e.g. writen to main memory) the start of the next
        logical sector will have passed the read/write head and will
        not be accessible until the disk's rotation brings it back
        under the head.
     
        Staggering the physical sectors (e.g. 0,3,6,1,4,7,2,5,8) aims
        to allow just enough time deal with one sector before the next
        is accessible.  This obviously depends on the relative speed
        of the rotation of the disk, sector size, sectors per track
        and the speed of transfer of sectors to main memory.