code: function( cylinder, head, sector ) {
  
      if( this.headsPerTrack < 0 || this.sectorsPerTrack < 0 )
        throw new Error( 'Unspecified device geometry' )
  
      return ( cylinder * this.headsPerTrack + head ) *
        this.sectorsPerTrack + ( sector - 1 )
  
    }
docs: Converts a CHS address to an LBA
  @param  {Number} cylinder
  @param  {Number} head
  @param  {Number} sector
  @return {BlockDevice}