== Layout Variants ==
Four variants of the file system layout has been identified. A summary diagram
can be found here: [ https: //github.com/wwylele/3ds-save-tool/raw/master/inner-fat.png]
=== Savegame, <code>duplicate data = true</code> ===
All free blocks that are not allocated to any files also form a node chain in the allocation table. The head index of this "free chain" is recorded in <code>FAT.Index_V</code>. Other fields of <code>FAT</code> are all zero
Here is an example: [
For extdata, because only two "files" (directory and file entry tables) are allocated in the data region, and their size never changes once the extdata is created, they are guaranteed continuous in the data region, and the FAT degenerates to two big nodes. Therefore, instead of going through FAT, the offset and size of directory / file entry table can be found directly by offset = entry_table_starting block * data_region_block_size + data_region_offset and size = entry_table_block_count * data_region_block_size.