fat.txt

汇编源代码大全

By: Inbar Raz
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 The FAT is a linked-list table that DOS uses to keep track of the physical
 position of data on a disk and for locating free space for storing new files.

 The word at offset 1aH in a directory entry is a cluster number of the first
 cluster in an allocation chain.  If you locate that cell in the FAT, it will
 either indicate the end of the chain or the next cell, etc.  Observe:

                                    starting cluster number --|
Directory +-------------------+-+-------------------+---+---+-+-+-------+
Entry -- |M Y F I L E   T X T|a|                   |tim|dat|08 | size  |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|-+-+-+-+-+
                                    +-------------------------+
    00  01  02  03  04  05  06  07  |8  09  0a  0b  0c  0d  0e  0f
   +--++--++--++--++--++--++--++--++-++--++--++--++--++--++--++--+
00 |ID||ff||03-04-05-ff||00||00||09-0a-0b-15||00||00||00||00|
   +--++--++--++--++--++--++--++--++--++--++--++|-++--++--++--++--+
                        +-----------------------+
   +--++--++--++--++--++-++--++--++--++--++--++--++--++--++--++--+
10 |00||00||00||00||00||16-17-19||f7||1a-1b-ff||00||00||00||00|
   +--++--++--++--++--++--++--++|-++--++-++--++--++--++--++--++--+
                                +-------+
This diagram illustrates the main concepts of reading the FAT.  In it: