anchor.diff:                             (aref buf (+ buf-idx 1)) (ldb (byte 8  8) byte-24)
                              (aref buf (+ buf-idx 2)) (ldb (byte 8 16) byte-24))))
                    )))
  -            (block-device-write disk (+ sector fat-offset) 1 buf)))))
  +            (write-fat-sectors disk 0 fat12 fat-offset sector buf)))))
       (setf (aref dirty-bits 0) 0)))
   
   (defmethod read-fat (disk (fat16 fat16) &optional fat-array)
  
positive.code:                                                        :element-type '(unsigned-byte 32)
                                                         :initial-element 0))
           (return fat)))
  
  (defmethod write-fat (disk (fat12 fat12) fat)
    (let* ((dirty-bits (fat-%fat-dirty-bits fat12))
  
negative.code:                      (word-offset (* sector clusters-per-sector)))
                  (dotimes (i clusters-per-sector)
                    (setf (sys.int::ub32ref/le buf (* 4 i)) (aref fat (+ word-offset i))))
                  (write-fat-sectors disk (fat32-%flags fat32) fat32 fat-offset sector buf)))))
          (setf (aref dirty-bits word-idx) 0)))))
  
  (defun fat-value (fat idx)
  