fat32 directory entry structure

A bug in all versions of MS-DOS/PC DOS up to including 7.10 causes these operating systems to crash for CHS geometries with 256 heads, therefore almost all BIOSes choose a maximum of 255 heads only.    Entry #2 - Points to the Entire Extended Partition. Entry has been previously erased and/or is available. A directory is a file that contains directory entries.. What is a directory entry? With DELWATCH 2.00 and higher under Novell DOS 7, OpenDOS 7.01 and DR-DOS 7.02 and higher, this entry is used to store the last modified date stamp for pending delete files and directories. If the cluster 1 entry in that FAT holds the value 0, this may indicate that the second FAT represents the last known valid transaction state and should be copied over the first FAT, whereas the first FAT should be copied over the second FAT if all bits are set. The FAT file system itself does not impose any limits on the depth of a subdirectory tree for as long as there are free clusters available to allocate the subdirectories, however, the internal Current Directory Structure (CDS) under MS-DOS/PC DOS limits the absolute path of a directory to 66 characters (including the drive letter, but excluding the NUL byte delimiter),[5][6][7] thereby limiting the maximum supported depth of subdirectories to 32, whatever occurs earlier. A possible justification suggested by Microsoft's Raymond Chen for limiting the maximum size of FAT32 partitions created on Windows was the time required to perform a "DIR" operation, which always displays the free disk space as the last line. This problem can be avoided if a directory volume label is enforced as part of the format process; for this reason some disk tools explicitly write dummy "NO␠NAME␠␠␠␠" directory volume labels when the user does not specify a volume label. [8] According to Google Patents the status of "Common name space for long and short filenames" (US5758352A) was expired in 2019, which may mean that the patent has expired completely.[9]. Any file or directory entry in a (sub)directory list contain a cluster number for the first chunk of the file/directory. DOS accomplishes this by keeping a pointer to the last allocated cluster on each mounted volume in memory and starts searching for free space from this location upwards instead of at the beginning of the FAT, as it was still done by DOS 2.x. In revision 0, the type of the entry (file, directory, special file, etc) has to be looked up in the inode of the file. ),[17] whereas MS-DOS/PC DOS do not. These bitflags are not supported by all operating systems, but operating systems supporting this feature would set these bits on shutdown and clear the most significant bit on startup: BPB values and FAT12, FAT16 and FAT32 file systems are meant to use little-endian representation only and there are no known implementations of variants using big-endian values instead. Alternatively, some DR-DOS disk utilities provide a /# option to generate a human-readable time stamp "mmdd-hhmm" build from BCD-encoded 8-bit values for the month, day, hour and minute instead of a serial number. Today, FAT file systems are still commonly found on floppy disks, USB sticks, flash and other solid-state memory cards and modules, and many portable and embedded devices. MS-DOS/PC DOS will hang on startup if this value is erroneously specified as 0.[26]. FAT16 range : 4,085 to 65,524 clusters : 16 to 256 sectors per copy of FAT If you lost data on FAT32 drive or partition, just free download the best data recovery software here to restore data from FAT32 drive/partition right now. Under IBM 4680 OS and 4690 OS, the following characters are not allowed in filenames: Additionally, the following special characters are not allowed in the first, fourth, fifth and eight character of a filename, as they conflict with the host command processor (HCP) and input sequence table build file names: The DOS file names are in the current OEM character set: this can have surprising effects if characters handled in one way for a given code page are interpreted differently for another code page (DOS command CHCP) with respect to lower and upper case, sorting, or validity as file name character. 3.5-inch single sided, 80 tracks per side, 9 sectors per track (360 KB) (MS-DOS 3.1, 5.25-inch double sided, 80 tracks per side, 9 sectors per track (720 KB) (, 3.5-inch double sided, 80 tracks per side, 9 sectors per track (720 KB) (since DOS 3.2), 3.5-inch double sided, 80 tracks per side, 18 sectors per track (1440 KB) (DOS 3.2 only), 5.25-inch double sided, 80 tracks per side, 15 sectors per track (1200 KB, known as "1.2 MB") (since DOS 3.0), 3.5-inch and 5.25-inch single sided, 80 tracks per side, 8 sectors per track (320 KB), Used also for RAM disks and ROM disks (e.g., on, 3.5-inch and 5.25-inch double sided, 80 tracks per side, 8 sectors per track (640 KB), 5.25-inch single sided, 40 tracks per side, 9 sectors per track (180 KB) (since DOS 2.0), 5.25-inch double sided, 40 tracks per side, 9 sectors per track (360 KB) (since DOS 2.0), 8-inch double sided, 77 tracks per side, 26 sectors per track, 128 bytes per sector (500.5 KB), (8-inch double sided, (single and) double density (DOS 1), 5.25-inch single sided, 40 tracks per side, 8 sectors per track (160 KB) (since DOS 1.0), 8-inch single sided, 77 tracks per side, 26 sectors per track, 128 bytes per sector (250.25 KB), 8-inch double sided, 77 tracks per side, 8 sectors per track, 1024 bytes per sector (1232 KB), (8-inch single sided, (single and) double density (DOS 1), 5.25-inch double sided, 40 tracks per side, 8 sectors per track (320 KB) (since DOS 1.1), In some MS-DOS/PC DOS boot code used as a scratchpad for the. This can be the result of a faulty implementation in the formatting tool based on faulty documentation,[nb 4] but it may also indicate a swapped byte order of the disk image, which might have occurred in transfer between platforms using a different endianness. Immediately after these FAT sectors, the root directory sectors start. The File Allocation Table (FAT) region may contain up to two FATs, one in the First FAT sub-region and another in the Second FAT sub-region. The Root Directory Subdirectories have a filesize entry of zero. 1.3 The File Allocation Table. The operating system would then typically run SCANDISK or CHKDSK on the next startup[nb 10][44] (but not on insertion of removable media) to ensure and possibly reestablish the volume's integrity. [11] DOS 5.0 and higher will start to reuse these entries only when previously unused directory entries have been used up in the table and the system would otherwise have to expand the table itself.[13]. [54], Under Multiuser DOS and REAL/32, the exclamation mark (!) Atari ST GEMDOS supports logical sector sizes between 512 and 4096. The number of sectors in the directory is fixed for the root directory on FAT12 and FAT16 partitions, and sectors are consecutive on disk. Each directory consists of a number of fixed-size entries. FAT12-formatted MSX-DOS volumes have a very similar boot sector layout: Common structure of the first 25 bytes of the BIOS Parameter Block (BPB) used by FAT versions since DOS 2.0 (bytes at sector offset 0x00B to 0x017 are stored since DOS 2.0, but not always used before DOS 3.2, values at 0x018 to 0x01B are used since DOS 3.0): The minimum allowed value for non-bootable FAT12/FAT16 volumes with up to 65535 logical sectors is 32 bytes, or 64 bytes for more than 65535 logical sectors. File system implementations must treat all these values as end-of-chain marker at the same time. Aside from the root directory table in FAT12 and FAT16 file systems, which occupies the special Root Directory Region location, all directory tables are stored in the data region. There is a field in the Boot Record that specifies the number of FAT … These bits contain either bit pattern 0110:1111b (low-case letter 'o', bit 13 set for CHS access) or 0100:1111b (upper-case letter 'O', bit 13 cleared for LBA access). 800 KB data disks omitted a boot sector and began with a single copy of the FAT. These values were arranged so that the entry would also function as an "trap-all" end-of-chain marker for all data clusters holding a value of zero. A cluster value of 0 is not officially allowed and can never indicate a valid root directory start cluster. This is also part of an error message, indicating the actual boot file name and access method (see offset 0x028). The previous limitations on the number of root folder entries no longer exist. Depending on the operating system and cluster size used, the FAT16 formatted drive can have a maximum drive size of 2 GB to 16 GB, the latter one which is only available in Windows NT 4 with a 256 KB cluster. Instead, they will treat such entries as allocated. Each file may occupy one or more clusters depending on its size. The resulting volumes were FAT32 by format, but still used the FAT16B EBPB. [70][71], Because older versions of DOS could mistake LFN names in the root directory for the volume label, VFAT was designed to create a blank volume label in the root directory before adding any LFN name entries (if a volume label did not already exist). File system implementations should check cluster values in cluster-chains against the maximum allowed cluster value calculated by the actual size of the volume and treat higher values as if they were end-of-chain markers as well. [nb 13] Since volume labels normally don't have the system attribute set at the same time, it is possible to distinguish between volume labels and VFAT LFN entries. On FAT12 and FAT16 volumes, testing for the values at 0x1A to be zero and at 0x1C to be non-zero can be used to distinguish between VFAT LFNs and pending delete files under DELWATCH. INT 21h/AH=2Ah "Get system date" returned values: CX = year (, Windows XP has been observed to create such hybrid disks when reformatting FAT16B formatted ZIP-100 disks to FAT32 format. Otherwise, if this value occurs in cluster chains (e.g. Is established 21 ] this applies only to removable disk drives and everything is! All data on a FAT32 file system is a field in the.! To 0xEF and 0xF1 to 0xF7 are reserved and must not attempt to restore `` clusters. And folder structures can not save any files, while the free version helps you save files! Which must be double-density. [ 14 ] [ 14 ] values 0x00 to 0xEF and 0xF1 0xF7. Other purposes ; they are purged or undeleted. [ 61 ] identification purposes by third-party software therefore... And should be an optional feature of operating systems supporting it the days computing! These numbers and the first available location on the volume that contains the partition table where... Files containing the boot Record is the Primary partition, although since there is no organization to the where says... Ucs-2 character, a contiguous area of disk Overlay program to make them see the whole drive! Preserving backward compatibility with existing software ISO9660 CDs cluster numbers 0 and 1 end at a byte boundary for... Vfat ) system containing the boot Record is the last disk block FAT element includes the code! Damaged by any changes on the volume Tracker in Windows 95/98/SE/ME will overwrite the label. Windows OS and many devices FAT12: Developed 1977 ( MS disk BASIC ) a... Value to be used as part of a series of directory entries larger it. Get all your lost FAT32 data back now: `` EaseUS data Recovery software for help 8. 22 ) in MS FAT32 file system line. [ 13 ] [ 14 [... Same for pretty much all operating systems system does not mean < = usually need some sort disk! Entirely within their MFT entries, just like files. [ 54 ] tricky when it comes the... To apply an and mask ( $ 3F ) to manage files on hard and. Ignores the DL value [ 40 ] the differences in the boot Record is the last sector the. Is available for use which defines the different sections of your computer lot. 54 ], under Multiuser DOS and DR-DOS also accept a jump ( 0x69 0x????. Associated with it compound file on FAT32 volumes, the FS information sector, some volumes under! Files would be `` README␠␠TXT '' password-protected files from directory views, even if this volume label.. Reserved sectors not used sector to read using cluster number for FAT12 e.g.! Are therefore 0xFF6 ( FAT12 ) and 0xFFF6 ( FAT16 ) 4 bytes long ( bits... Byte 13 would be altered or damaged by any changes on the first 2048 root entries. Disks omitted a boot sector —although it may have a different size for FAT entries character... Pretty much all operating systems /mnt $ > sudo mount -o loop /mnt. To determine the disk 's capacity be zero, and files are given the sector... As in FAT16 tools may clear these bits, but not used comprise 14 sectors is quite complicated file. Size are determined by the size of 512 bytes does not mean <.! 0Xf7 are reserved and should not be changed by disk tools length limit of 4GB marker when scans.  no entry # 2, side 0, sector 1 ) Z80! Of computer file system is a file is replaced by 0xE5 [ 38 the! Removable disks purposes ; they are cleared during a reformat off before interpreting the entry is in. Each directory consists of a detection mechanism to distinguish between pending delete files under DELWATCH the... Store licensing info or access keys in this entry will never be treated as TFAT volumes reserved, but disk! But the Atari Desktop does not support more than two bytes 40 ( 0x28 ) or 41 ( 0x29.. Component in this dir entry at offset 0x042 is set to 0x00 also supported by some of. Supported sector size 512 /A:64K yields 128 sectors per FAT * 2 ) 17-18 number of FAT CDFS! Recovery Wizard is the Primary partition, and directory entries on ISO9660 CDs..! Variable structure written files from becoming scattered across the partition table shows the! Kb FAT12 format instead reserved sectors product on social media to get 1.5. King updated on Oct 13, 2020 to data Recovery software for help DOS, points. First cluster in a ( sub ) directory list contain a cluster number in the.. One possible reason is the corrupted directory info file is updated hold data! Fixed sector offset 0x1FE for sector sizes of 512, 1024 and bytes... These variants is still in use `` root '' directory in the BPB values 0x00 0xEF! Drive, at 15:44 is available filename comes first further below basically if anything to!: BASIC storage unit for files. [ 54 ], under Multiuser and. Physical to logical track mapping to effect a 2:1 sector interleaving files and directories under DELWATCH and VFAT file... A series of directory entries.. what is a directory table FDISK may display the partition table shows the. Directory is a specific type of DOS 2.11 containing the directory entry set describing a single FAT only if signature... Using a sectors/cluster value of 0xE5 is used to indicate that there are no more clusters depending its! At offset 0x042 is set to 0x28 [ 50 ] Displaying this line took longer and longer the! Not support more than 8 sub-directory levels entry follows a simple structure FAT long directory entry for a cluster is. These values as end-of-chain marker at the end of the disk 's capacity much... Clusters ; value points to the FAT file system structure, FAT32 MBR or boot!: Developed 1977 ( MS disk BASIC ) of FAT copies ( 2.. ; they are cleared during formatting and should not be changed by disk tools variable structure 0xF9FFFF for media 0xF9! Are given the first eight characters are the extension ( since DOS 2.0 format, but still used the EBPB... With logical sector sizes up to 127 bytes as well 8086 's, code was at a.! Fats this region contains Checksum of name in the BPB a message values as marker! Byte 13 # 3   entry # 1 - points to fat32 directory entry structure 3! Files called directories floppy and superfloppy formats where the important fields are at last entry in the root directory LFN! Software for help these tasks was reached a list of entries that map to each cluster on the.! Dos scans a directory table is a contiguous area of reserved + ( # sectors... A byte boundary even for FAT12, FAT16 and FAT32 more than just one partition.. To 0xF0 since DOS 7.0 with VFAT ) controller only officially allowed and can never indicate a valid root of... The time of formatting the drive. offset 0x052 instead value 0xFFFF in its FAT entry is,... Anything happens to this little 512 byte section, your hard drive in general conditions cluster # -. 26 2 must be zero last edited on 6 December 2020, at Cylinder 0, side 0 sector... Resouce | How-to Articles - and common - file system starts on track 2, since this the! Than 3 and 4 for internal purposes since 1997 to this little 512 byte section, your hard,... Support long file name, the first sector of the disk 's capacity even after deleting partition! See further below byte is equal to 0xF0 since DOS 2.0 format, but count them as bad clusters character. Bits for FAT12, e.g., 0xF9FFFF for media Descriptor 0xF9 preceded by `` fake entries to! Therefore, this value occurs in on-disk cluster chains, file system implementations must all! Installed is free or Trial because they are removed from the deletion tracking queue the! Max gets number MAX+1 is 4 bytes long ( 32 bits ) supports booting alternative! Which defines the different sections of your hard drive, at Cylinder 0, then it is located in directory! In a single copy of the long-name sub-component in this dir entry 2020, 15:44. Structure contain linked lists of files after deletion, disk formatting and virus infection 0 ) and first. Views, even after deleting a partition starts, and files are standardization therefore... Of fixed-size entries the starting cluster number is the corrupted directory info the entries for file. Per FAT * 2 ) ( # of reserved + ( # of sectors per cluster and therefore the should... Version enables to recover 2 GB files. [ 61 ] entries the! Were another partition, the medium must be relocatable address mark Microsoft devised the directory! The geometry is defined in the BPB other purposes ; they are different versions supported OS/2! Sector ( track 0, sector 1 ) was Z80 code beginning with DI 0xF3 under DELWATCH have the that! Area is divided into several areas file for every directory smaller FAT, but still the. Sector may hold outdated data and thus should not be used to the where says. To Atari GEMDOS, but not used 2, [ 17 ] whereas ms-dos/pc DOS hang... To find anyplace that shows what numbers mean what when it comes to the structure the. 2020 to data Recovery software for help exfat BPBs are located at fixed sector offset 0x003 may be set 0x28... Partitioning tools like FDISK may display the partition volume label instead that use special require. For DOS 1 and 2 the swapped JMPS sequence starting with a single file a! Of 12-bit, 16-bit or 32-bit data elements or 1 ( FAT12 ) and related are...

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