DOS3 File System

Boot sector

Sectors $01-$09 is boot sector.
$0A-$0F are empty.

Directory

$10-$17 are directory. I don't know what's first entry, containing $0E empty bytes and $7F $A5 at the end (for MD) and $57 $A5 for SD.

Offset Description

$00 Flags
bit 0 Unknown

bit 1 Unknown

bit 2 Unknown

bit 3 Unknown

bit 4 Unknown

bit 5 Unknown

bit 6 Unknown

bit 7 Unknown

$01-$08 Filename (padded by spaces)

$09-$0B Extension (padded by spaces)

$0C Number of blocks (8 sectors)

$0D Starting block

$0E-$0F Length of file in bytes

Offset	Description
$00	Flags
	bit 0	Unknown
	bit 1	Unknown
	bit 2	Unknown
	bit 3	Unknown
	bit 4	Unknown
	bit 5	Unknown
	bit 6	Unknown
	bit 7	Unknown
$01-$08	Filename (padded by spaces)
$09-$0B	Extension (padded by spaces)
$0C	Number of blocks (8 sectors)
$0D	Starting block
$0E-$0F	Length of file in bytes

FAT

Sector $18 is FAT. Maximum number of blocks that could be allocated is $7F.

$FF - can't be allocated
$FE - free
$FD - eof
other - link to other block

This format is just guessed.