FATX - Filesystem
FATX is the file system used by the Xbox and the Xbox 360, it is unsupported natively by Windows but has some functionality in Linux. Sometimes called "XTAF" (due to its little endian header), the file system is derived from the age-old MS-DOS file system and can be considered as a cleaned-up version of it.
Note that, while not part of the file system itself, the media which contain this file system do not have a master file table which describes which file system starts where. It is up to the consumer Xbox 360, geom_xbox360 kernel module to know this.
File System Layout
The file system is divided into 4 parts:
- Header (the BOOT sector on FAT file systems)
- File allocation table (FAT)
- Root directory cluster/data region
All multi-byte values contained in each part are 1 big-endian.
Difference Between Retail and Development Kit HDD
The essential difference between retail and devkit HDDs is that devkit HDDs hold a partition table (length of 0x18 bytes) at the start of the drive. The table contains sector and length information for the Content and DEVKIT Partitions (possibly Compatibility partition too). This partition table only exists on Devkit HDDs, retails have the offsets built in to the kernel.
USB Drive Layout
Unlike the hard disks and memory units that the Xbox 360 originally shipped with, the USB drives which can be Xbox 360-configured contain sets of files located in a hidden "Xbox360" folder located in the root of the device. The Data0000-Data0003 files are always present no matter what the device size. The Data0000 file houses the Cache/USB System Extended partitions, device performance information, and device geometry (mainly just the total device size). Data0001 contains the file allocation table for the Data partition, which uses the remaining files.
There was some research done in hopes to remove the maximum device size of 16 GB (for Xbox 360 storage) on exploited/development consoles, but it was later discovered that anything a few GB larger than the current maximum causes the console to crash. http://www.xboxhacker.org/index.php?topic=16913.0
Configuration file
The configuration is the first 2 sectors (0x400 bytes) of the Data0000 and is created when the device is configured. It contains info about the device and is secured with a signature. The layout is as follows:
Type 1 (Certificate size = 0x228)
| Offset | Length | Description |
|---|---|---|
| 0 | 0x1A8 | Console Security Certificate |
| 0x1A8 | 0x80 | Signature (part of the console cert) |
| 0x228 | 0x14 | Device ID |
| 0x23C | 4 (UINT32) | Certificate size (0x228) |
| 0x240 | 8 (UINT64) | Size of device in bytes |
| 0x248 | 2 (UINT16) | Read speed in KBs |
| 0x24A | 2 (UINT16) | Write speed in KBs |
| 0x24C | 0x1B4 | Padding (0x00) |
Type 2 (Certificate size = 0x100)
| Offset | Length | Description |
|---|---|---|
| 0 | 0x100 | Device Signature |
| 0x100 | 0xA8 | Padding (0x00) |
| 0x228 | 0x14 | Device ID |
| 0x23C | 4 (UINT32) | Certificate size (0x100) |
| 0x240 | 8 (UINT64) | Size of device in bytes |
| 0x248 | 2 (UINT16) | Read speed in KBs |
| 0x24A | 2 (UINT16) | Write speed in KBs |
| 0x24C | 0x1B4 | Padding (0x00) |
The signature is derived from a SHA1 hash taken from the start of the device id (0x228) till the end of the config (0x1D8 bytes) and is signed with the consoles private key and the matching public parameters are present in the console certificate for verification later on.
The certificate size is used to determine how to verify the configuration file when the device is mounted. If the value is 0x228 then the device was configured by an Xbox and the signature is verified using the params in the console certificate, if the value is 0x100 then the device was pre-configured by Microsoft and is verified using the SATA public key (also used for HDDSS verification).
The last 2 values are written when the device is configured, it is unknown how these are used later on. Perhaps it could be used to determine what connected device would provide best performance for caching.
Partition Header
For each offset, add the offset of the partition.
| Offset | Length | Type | Information |
|---|---|---|---|
| 0x0 | 0x4 | ascii string | Partition magic (XTAF) |
| 0x4 | 0x4 | unsigned int | Partition ID |
| 0x8 | 0x4 | unsigned int | Sectors per Cluster |
| 0xC | 0x4 | unsigned int | Root directory cluster |
SysExt Partition
The SystemUpdate with Kernel-Version 2.0.12611.0 (Kinect-Dashboard) introduced a new system to hold the Kinect-/Avatar related systemfiles. It creates a Partition named "SysExt" aka SystemExtended to store these files. You could call it a Sub-Partition or Hidden-Partition as it's a "Partition inside another Partition".
Partition Locations
Memory Unit
| Offset | Length | Information | Format |
|---|---|---|---|
| 0x0 | 0x7FF000 | System Cache | SFCX |
| 0x7FF000 | end of drive | Data | FATX |
Xbox 360 Hard Drive
| Offset | Length | Information | Format |
|---|---|---|---|
| 0x2000 | 0x204 - 0x80000 | Security Sector | Binary |
| 0x80000 | 0x80000000 | System Cache | SFCX |
| 0x80080000 | 0xA0E30000 | Game Cache | SFCX |
| 0x10C080000 | 0xCE30000 | SysExt | FATX ("Sub"-Partition) |
| 0x118EB0000 | 0x8000000 | SysExt2 | FATX ("Sub"-Partition) |
| 0x120eb0000 | 0x10000000 | Xbox 1 Backwards Compatibility | FATX |
| 0x130eb0000 | end of drive | Data | FATX |
Development Kit HDD Partition Table
| Offset | Length | Information | Value |
|---|---|---|---|
| 0x0 | 0x4 | HDD Header (Devkit identification) | 0x00020000 |
| 0x4 | 0x4 | ? | ? |
| 0x8 | 0x4 | Content Volume sector | 0x00633000 (Raw address: 0xC6600000 = 0x633000 * 0x200) |
| 0xC | 0x4 | Content Volume length (in sectors) | variable (real length = var * 0x200) |
| 0x10 | 0x4 | Xbox 360 Dashboard Volume sector | 0x005B3000 (Raw address: 0xB6600000 = 0x5B3000 * 0x200) |
| 0x14 | 0x4 | Xbox 360 Dashboard Volume length (in sectors) | 0x00080000 (0x10000000 = 0x80000 * 0x200) |
USB Drive
| Offset | Length | Information | Format |
|---|---|---|---|
| 0x8000400 | 0x12000400 | System Cache | FATX |
| 0x8115200 | 0x8000000 | SysExt ("Sub"-Partition) | FATX |
| 0x12000400 | 0xDFFFC00 | SysExt2 ("Sub"-Partition) | FATX |
| 0x20000000 | End of Files | Data | FATX |
"Josh" Sector
The "Josh" Sector is located on the 4th sector (0x800). It's purpose is currently unknown. It may be used just to identify the Xbox that previously formatted it.
| Offset | Length | Type | Information |
|---|---|---|---|
| 0x0 | 0x4 | ascii string | "Josh" magic |
The Console Security Certificate(Inc 0x80 sig) then,
| Offset | Length | Type | Information |
|---|---|---|---|
| 0x22C | 0x24 | STFSVolumeDescriptor | Cache? |
| 0x250 | 0x24 | STFSVolumeDescriptor | Cache? |
| 0x274 | 0x4 | (un?)signed int | Unknown |
| 0x278 | 0x4 | (un?)signed int | Unknown |
| 0x27C | 0x4 | unsigned int | TitleID(for the first VolumeDescriptor) |
| 0x280 | 0x4 | unsigned int | TitleID(for the second VolumeDescriptor) |
The upper 4 bits in the STFSVolumeDescriptor.Flags seem to always be set (maybe to signify it is cache)
Security Sector
The Security Sector is used by Microsoft to verify that the harddrive is an original Microsoft product. The Security Sector holds details such as drive sector count, drive serial number and the Microsoft logo (to stop other companies using it)
It begins at the 16th sector on the drive (0x2000).
| Offset | Length | Type | Information |
|---|---|---|---|
| 0x0 | 0x14 | ascii string | Serial Number |
| 0x14 | 0x8 | ascii string | Firmware Revision |
| 0x1C | 0x28 | ascii string | Model Number |
| 0x44 | 0x14 | bytes | MS Logo Hash |
| 0x58 | 0x4 | unsigned int (LITTLE ENDIAN) | Number of Sectors on drive |
| 0x5C | 0x100 | bytes | RSA Signature |
| 0x200 | 0x4 | signed int | MS Logo Size |
| 0x204 | MS Logo Size | image | MS Logo |
If a Security Sector from a smaller hard drive is used on a bigger one, the Xbox will only see the number of sectors defined in the Security Sector.
Chainmap and directories
To find the offset of the chainmap, take the offset of the position and add 4096 (0x1000) to it. Each entry in the chainmap is either an unsigned int or a unsigned short, depending on the number of clusters inside the partition.
To work out the cluster size, take the Sectors per Cluster value and multiply it by 512 (0x200).
To work out the number of clusters, divide the partitions size by the cluster size and that's have the number of clusters.
If the number of clusters is below 65520 (0xFFF0), then the drive uses 2-byte chainmap entries, otherwise it uses 4-byte chainmap entries. The size of the chainmap is the size of the chainmap entries multiplied by the partitions cluster count.
To get a clusters offset, you need to work out the offset of the file data area. This is determined by taking the chainmap offset and adding it's size to it. You then simply times the cluster index (minus 1) by the cluster size and add it to the file data offset.
To get a clusters chainmap entrys offset, times the cluster index by the chain map entry size and add that to the chainmap offset.
Files
The file contents is stored per cluster as indicated by the chainmap and the starting cluster (see below). If the file is larger than one cluster, it is stored in multiple clusters. If the length of the file is not a multiple of the cluster size, then the last cluster is only partially used. If the file covers more than 1 cluster, the next cluster must be determined by finding the current cluster's entry in the chainmap and using the value as the next cluster.
Directories
Directories are stored in a tabular format. Because directories are normal files with the "directory" bit set, they are allocated in the FAT and may therefore cover multiple clusters. This makes it possible to have many files in one directory.
Each entry of the directory table is 64 bytes long.
An entry can be set to all 0xFF bytes, which means that this entry is unused and probably marks the end of the directory contents. Used entries are filled as follows:
| Offset | Type | Size | Description |
|---|---|---|---|
| 0x00 | byte | 1 | File name length, or 0xE5 for deleted files |
| 0x01 | byte | 1 | File Attributes |
| 0x02 | ASCII string | 0x2A | file name, padded with either 0x00 or 0xFF bytes |
| 0x2C | unsigned int | 4 | First cluster of file, null/0x00 for empty files |
| 0x30 | (un?)signed int | 4 | File size |
| 0x34 | (un?)signed short? | 2 | Creation date |
| 0x36 | (un?)signed short? | 2 | Creation time |
| 0x38 | (un?)signed short? | 2 | Last write date |
| 0x3A | (un?)signed short? | 2 | Last write time |
| 0x3C | (un?)signed short | 2 | Last access time |
| 0x3E | (un?)signed short | 2 | Last access time |
The file flags and the date and time fields are in the same format as the one used in the FAT file system. For time, bits 15-11 represent the hour, 10-5 the minutes, 4-0 the seconds. For date, bits 15-9 are the year, 8-5 are the month, 4-0 are the day.
The volume bit is unused, the volume label is instead stored in a file "name.txt" in the root directory. The contents of this file is big-endian UTF-16 (Unicode string) starting at offset 0x2
The following characters are found in XTAF file names from actual disk images:
- 0x20, 0x24, 0x2e ( SPACE $ . )
- 0x30-0x39 (digits 0-9)
- 0x41-0x5a (letters A-Z)
- 0x5f ( _ )
- 0x61-0x7a (letters a-z)
Unlike the FAT file system, XTAF has no "." and ".." entries in the directory tables. This means that it's only possible to go to the parent directory by remembering its cluster number.
Limitations
| Attribute | Limitation |
|---|---|
| Maximum Filename Length | 0x2A (42) |
| Maximum Path Length | 240 Characters |
| Maximum File Size | 4 GB (4294967296 bytes) |
| Maximum File Per Directory | 0x1000 (4096) |
| File/Folder Name Characters | ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789 |
Possible cluster sizes
- 4 KB (0x1000 bytes, 0x8 sectors per cluster)
- 8 KB (0x2000, 0x10 SPC)
- 16 KB (0x4000, 0x20 SPC)
- 32 KB (0x8000, 0x40 SPC)
- 64 KB (0x10000, 0x80 SPC)