The fx-CG20 uses a FAT16.
The directory is very similar to the PC DOS directory structure.
The directory does not reside at a fixed position.
A directory entry consists of 32 bytes:
0x20: file (archive bit; set on whenever a file has been written to and closed)
Formerly the file time
Formerly the file date.
The starting cluster number (little endian)
File size (little endian)