anchor.diff:            (fat-%sectors-per-cluster ffs) (check-sectors-per-cluster (aref sector 13) bytes-per-sector)
             (fat-%n-reserved-sectors ffs) (sys.int::ub16ref/le sector 14)
             (fat-%n-fats ffs) n-fats
  -          (fat-%n-root-entry ffs) (sys.int::ub16ref/le sector 17)
             (fat-%n-sectors16 ffs) (sys.int::ub16ref/le sector 19)
             (fat-%media-type ffs) (check-media-type (aref sector 21))
             (fat-%sectors-per-track ffs) (sys.int::ub16ref/le sector 24)
  
positive.code:                                :drive-n (aref sector 36) ; Operating system specific
                                 :boot-code (subseq sector 62 510))))
      (when (check-signature (aref sector 38))
        (setf (fat-%signature fat16) (aref sector 38)
              (fat-%volume-id fat16) (sys.int::ub32ref/le sector 39)
              (fat-%volume-label fat16) (map 'string #'code-char (subseq sector 43 54))
              (fat-%fat-type-label fat16) (map 'string #'code-char (subseq sector 54 60))))
  
negative.code:           (fat-%n-clusters ffs) (+ (compute-cluster-count sector) 2))))
  
  (defclass fat12 (fat-base)
    ((%n-root-entry :initarg :n-root-entry :accessor fat-%n-root-entry :type (unsigned-byte 16))))
  
  (defun check-signature (signature)
    (if (or (= signature #x28)
  