File System Comparison

File System Comparison

General information

File system / Creator / Year of introduction / Original operating system
DECtape / DEC / 1964 / PDP-6 Monitor
Level-D / DEC / 1968 / TOPS-10
V6FS / Bell Labs / 1972 / Version 6 Unix
RT-11 / DEC / 1973 / RT-11
Disk Operating System (GEC DOS) / GEC / 1973 / Core Operating System
GEC DOS filing system extended / GEC / 1977 / OS4000
FAT12 / Microsoft / 1977 / Microsoft Disk BASIC
V7FS / Bell Labs / 1979 / Version 7 Unix
ODS-2 / DEC / 1979 / OpenVMS
DFS / Acorn Computers Ltd / 1982 / Acorn BBC MicroMOS
FFS / Kirk McKusick / 1983 / 4.2BSD
MFS / Apple Computer / 1984 / Mac OS
HFS / Apple Computer / 1985 / Mac OS
Amiga OFS54 / Metacomco for Commodore / 1985 / Amiga OS
NWFS / Novell / 1985 / NetWare 286
Amiga FFS / Commodore / 1987 / Amiga OS 1.3
FAT16 / Microsoft / 1987 / MS-DOS 3.31
Minix V1 FS / Andrew S. Tanenbaum / 1987 / Minix 1.0
HPFS / IBMMicrosoft / 1988 / OS/2
JFS / IBM / 1990 / AIX11
VxFS / VERITAS / 1991 / SVR4.0
AdvFS / DEC / Before 1993 / Digital Unix
NTFS / Microsoft, Gary Kimura, Tom Miller / 1993 / Windows NT
LFS / Margo Seltzer / 1993 / Berkeley Sprite
ext2 / Rémy Card / 1993 / Linux
UFS1 / Kirk McKusick / 1994 / 4.4BSD
XFS / SGI / 1994 / IRIX
UDF / ISO/ECMA/OSTA / 1995 / -
FAT32 / Microsoft / 1996 / Windows 95b10
QFS / Sun Microsystems / 1996 / Solaris
GPFS / IBM / 1996 / AIX,Linux
Be File System / Be Inc., D. Giampaolo, C. Meurillon / 1996 / BeOS
Minix V2 FS / Andrew S. Tanenbaum / 1997 / Minix 2.0
HFS Plus / Apple / 1998 / Mac OS 8.1
NSS / Novell / 1998 / NetWare 5
PolyServe File System (PSFS) / PolyServe / 1998 / Windows, Linux
ODS-5 / DEC / 1998 / OpenVMS 7.2
ext3 / Stephen Tweedie / 1999 / Linux
JFS2 / IBM / 1999 / OS/2 WSeB
GFS / Sistina (Red Hat) / 2000 / Linux
ReiserFS / Namesys / 2001 / Linux
FATX / Microsoft / 2002 / Xbox
UFS2 / Kirk McKusick / 2002 / FreeBSD 5.0
OCFS / Oracle Corporation / 2002 / Linux
VMFS2 / VMware / 2002 / ESX
Fossil / Bell Labs / 2003 / Plan 9 from Bell Labs 4
Google File System / Google / 2003 / Linux
ZFS / Sun Microsystems / 2004 / Solaris
Reiser4 / Namesys / 2004 / Linux
Minix V3 FS / Andrew S. Tanenbaum / 2005 / MINIX 3
OCFS2 / Oracle Corporation / 2005 / Linux
NILFS / NTT / 2005 / Linux
VMFS3 / VMware / 2005 / ESX
GFS2 / Red Hat / 2006 / Linux
ext4 / Andrew Morton / 2006 / Linux
exFAT / Microsoft / 2006 / Windows CE 6.0
File system / Creator / Year of introduction / Original operating system

Limits

/ Maximum filename length / Allowable characters in directory entries25 / Maximum pathname length / Maximum file size / Maximum volume size 4
DECtape / 6.3 / A-Z, 0-9 / DTxN:FILNAM.EXT = 15 / 369,280 bytes (577 * 640) / 369,920 Bytes (578 * 640)
Level-D / 6.3 / A-Z, 0-9 / DEVICE:FILNAM.EXT[PROJCT,PROGRM] = 7 + 10 + 15 = 32; + 5*7 for SFDs = 67 / 34,359,738,368 words (2**35-1); 206,158,430,208 SIXBIT bytes / Approx 12 GB (64 * 178MB)
RT-11 / 12 bytes / A-Z, 0-9, $ / 16 bytes / 33,554,432 bytes (65536 * 512) / 33,554,432 Bytes
V6FS / 14 bytes 24 / Any byte except NUL and / 26 / No limit defined 12 / 8MiB57 / 2TiB
Disk Operating System (GEC DOS) / ? / ? / ? / ? at least 131072 bytes / ?
GEC DOS filing system extended / 8 bytes / A-Z, 0-9. Period was directory separator / ? No limit defined (workaround for OS limit) / ? at least 131072 bytes / ?
V7FS / 14 bytes 24 / Any byte except NUL and / 26 / No limit defined 12 / 1GiB58 / 2TiB
FAT12 / 255 bytes 24 / Any Unicode except NUL 2426 / No limit defined 12 / 32MiB / 1MiB to 32MiB
FAT16 / 255 bytes 24 / Any Unicode except NUL 2426 / No limit defined 12 / 2GiB / 16MiB to 4GiB
FATX / 42 bytes 24 / ASCII. Unicode not permitted. / No limit defined 12 / 2GiB / 16MiB to 2GiB
Fossil / ? / ? / ? / ? / ?
MFS / 255 bytes / Any byte except: / No path (flat filesystem) / 256MiB / 256MiB
HFS / 31 bytes / Any byte except: / Unlimited / 2GiB / 2TiB
FAT32 / 255 bytes 24 / Any Unicode except NUL 2426 / No limit defined 12 / 4GiB / 512MiB to 2TiB7
HPFS / 255 bytes / Any byte except NUL 27 / No limit defined 12 / 2GiB / 2TiB13
NTFS / 254 characters + "." / Any Unicode except NUL, / or: / 32,767 Unicode characters with each path component (directory or filename) up to 255 characters long 12 / 16EiB55 / 16EiB55
HFS Plus / 255 UTF-16 characters 1 / Any valid Unicode226 / Unlimited / 16EiB / 16EiB71
FFS / 255 bytes / Any byte except NUL 26 / No limit defined 12 / 4GiB / 256TiB
UFS1 / 255 bytes / Any byte except NUL 26 / No limit defined 12 / 4GiB to 256TiB / 256TiB
UFS2 / 255 bytes / Any byte except NUL 26 / No limit defined 12 / 512GiB to 32PiB / 1YiB
ext2 / 255 bytes / Any byte except NUL 26 / No limit defined 12 / 16GiB to 2TiB4 / 2TiB to 32TiB
ext3 / 255 bytes / Any byte except NUL 26 / No limit defined 12 / 16GiB to 2TiB4 / 2TiB to 32TiB
ext4 / Any byte except NUL 26 / No Limit defined 12 / 16GiB to 2TiB4 / 1024 PiB
GPFS / 255 (?) / Any byte except NUL 26 / No limit defined 12 / No limit found / 299 Bytes (2PiB tested)
GFS / 255 / Any byte except NUL 26 / No limit defined 12 / 2TB to 8EB63 / 2TB to 8EB63
ReiserFS / 4032 bytes/255 characters / Any byte except NUL 26 / No limit defined 12 / 8TiB8 (v3.6), 4GiB (v3.5) / 16TiB
Reiser4 / 3976 bytes / Any byte except / and NUL / No limit defined 12 / 8TiB on x86 / ?
OCFS / 255 bytes / Any byte except NUL 26 / No limit defined 12 / 8TiB / 8TiB
OCFS2 / 255 bytes / Any byte except NUL 26 / No limit defined 12 / 4PiB / 4PiB
XFS / 255 bytes / Any byte except NUL 26 / No limit defined 12 / 8EiB9 / 8EiB9
JFS / 255 bytes / Any byte except NUL 26 / No limit defined 12 / 8EiB / 512TiB to 4PiB
JFS2 / 255 bytes / Any Unicode except NUL / No limit defined 12 / 4PiB / 32PiB
QFS / 255 bytes / Any byte except NUL 26 / No limit defined 12 / 16EiB72 / 4PiB72
BFS / 255 bytes / Any byte except NUL 26 / No limit defined 12 / 12288 bytes to 260GiB3 / 256PiB to 2EiB
AdvFS / 255 characters / Any byte except NUL 26 / No limit defined 12 / 16TiB / 16TiB
NSS / 256 characters / Depends on namespace used 28 / Only limited by client / 8TiB / 8TiB
NWFS / 80 bytes 52 / Depends on namespace used 28 / No limit defined 12 / 4GiB / 1TiB
ODS-5 / 236 bytes15 / ? / 4096 bytes16 / 1TiB / 1TiB
VxFS / 255 bytes / Any byte except NUL 26 / No limit defined 12 / 16EiB / ?
UDF / 255 bytes / Any Unicode except NUL / 1023 bytes 43 / 16EiB / ?
ZFS / 255 bytes / Any Unicode except NUL / No limit defined 12 / 16EiB / 268EiB (2128 Bytes)
Minix V1 FS / 14 or 30 bytes, set at filesystem creation time / Any byte except NUL 26 / No limit defined 12 / 1GiB / 1GiB
Minix V2 FS / 14 or 30 bytes, set at filesystem creation time / Any byte except NUL 26 / No limit defined 12 / 1GiB / 1GiB
Minix V3 FS / 60 bytes / Any byte except NUL 26 / No limit defined 12 / 4GiB / 4GiB
VMFS2 / 128 / Any byte except NUL and / 26 / 2048 / 4TiB74 / 64TiB
VMFS3 / 128 / Any byte except NUL and / 26 / 2048 / 2TiB74 / 64TiB
Maximum filename length / Allowable characters in directory entries25 / Maximum pathname length / Maximum file size / Maximum volume size 4

Metadata

/ Stores file owner / POSIX file permissions / Creation timestamps / Last access/read timestamps / Last metadata change timestamps / Last archive timestamps / Access control lists / Security/ MAC labels / Extended attributes/ Alternate data streams/ forks / Checksum/ ECC
GPFS / Yes / Yes / Yes / Yes / Yes / No / Yes / Yes / Yes / Yes
DECtape / No / No / Yes / No / No / No / No / No / No / No
Level-D / Yes / Yes / Yes / Yes / Yes / Yes / Yes / No / No / No
RT-11 / No / No / No / Yes / Yes / No / No / No / No / No
V6FS / Yes / Yes / No / Yes / Yes / No / No / No / No / No
V7FS / Yes / Yes / No / Yes / Yes / No / No / No / No / No
FAT12 / No / No / Yes / Yes / No[1] / No / No / No / No 22 / No
FAT16 / No / No / Yes / Yes / No[1] / No / No / No / No 22 / No
FAT32 / No / No / Yes / Yes / No[1] / No / No / No / No / No
HPFS / Yes14 / No / Yes / Yes / No / No / No / ? / Yes / No
NTFS / Yes / No5 / Yes / Yes / Yes / No / Yes / ? / Yes / No
HFS / No / No / Yes / No / No / Yes / No / No / Yes / No
HFS Plus / Yes / Yes / Yes / Yes / Yes / Yes / Yes / ? / Yes / No
FFS / Yes / Yes / No / Yes / Yes / No / No / No / No / No
UFS1 / Yes / Yes / No / Yes / Yes / No / Yes 33 / Yes 33 / No 32 / No
UFS2 / Yes / Yes / Yes / Yes / Yes / No / Yes 33 / Yes 33 / Yes / No
LFS / Yes / Yes / No / Yes / Yes / No / No / No / No / No
ext2 / Yes / Yes / No / Yes / Yes / No / Yes 23 / Yes 23 / Yes / No
ext3 / Yes / Yes / No / Yes / Yes / No / Yes 23 / Yes 23 / Yes / No
ext4 / Yes / Yes / No / Yes / Yes / No / Yes 23 / Yes 23 / Yes / No
GFS / Yes / Yes / No / Yes / Yes / No / Yes 23 / Yes 23 / Yes / No
ReiserFS / Yes / Yes / No / Yes / Yes / No / Yes 23 / Yes 23 / Yes / No
Reiser4 / Yes / Yes / No / Yes / Yes / No / No / No / No / No
OCFS / No / Yes / No / No / Yes / Yes / No / No / No / No
OCFS2 / Yes / Yes / No / Yes / Yes / No / No / No / No / No
XFS / Yes / Yes / No / Yes / Yes / No / Yes / Yes 23 / Yes / No
JFS / Yes / Yes / Yes / Yes / Yes / No / Yes / Yes / Yes / No
QFS / Yes / Yes / Yes / Yes / Yes / Yes / Yes / No / Yes / No
BFS / Yes / Yes / Yes / No / No / No / No / No / Yes / No
AdvFS / Yes / Yes / No / Yes / Yes / No / Yes / No / Yes / No
NSS / Yes / Yes / Yes31 / Yes31 / Yes / Yes31 / Yes / ? / Yes1929 / No
NWFS / Yes / ? / Yes31 / Yes31 / Yes / Yes31 / Yes / ? / Yes1929 / No
ODS-5 / Yes / Yes / Yes / ? / ? / Yes / Yes / ? / Yes 17 / No
VxFS / Yes / Yes / Yes / Yes / Yes / No / Yes / ? / Yes 23 / No
UDF / Yes / Yes / Yes / Yes / Yes / Yes / Yes / No / Yes / No
Fossil / Yes / Yes 61 / No / Yes / Yes / No / No / No / No / No
ZFS / Yes / Yes / Yes / Yes / Yes / Yes / Yes / No 69 / Yes 60 / Yes
VMFS2 / Yes / Yes / No / Yes / Yes / No / No / No / No / No
VMFS3 / Yes / Yes / No / Yes / Yes / No / No / No / No / No
Stores file owner / POSIX file permissions / Creation timestamps / Last access/read timestamps / Last metadata change timestamps / Last archive timestamps / Access control lists / Security/ MAC labels / Extended attributes/ Alternate data streams/ forks / Checksum/ ECC

Features

/ Hard links / Soft links / Block journaling or / Metadata-only journaling / Case-sensitive / Case-preserving / File Change Log / Internal snapshotting/branching / XIP / Filesystem-level encryption
DECtape / No / No / No / No / No / No / No / No / No / No
Level-D / No / No / No / No / No / No / No / No / No / No
RT-11 / No / No / No / No / No / No / No / No / No / No
V6FS / Yes / No / No / No / Yes / Yes / No / No / No / No
V7FS / Yes / No 59 / No / No / Yes / Yes / No / No / No / No
FAT12 / No / No / No / No / No / No / No / No / No / No
FAT16 / No / No / No / No / No / Partial / No / No / No / No
FAT32 / No / No / No / No / No / Partial / No / No / No / No
HPFS / No / No / No / No / No / Yes / No / ? / No / No
NTFS / Yes / Yes34 / No37 / Yes37 / Yes36 / Yes / Yes / Yes / ? / Yes
HFS Plus / Partial / Yes / No / Yes48 / Partial35 / Yes / Yes64 / No / No / No77
FFS / Yes / Yes / No / No / Yes / Yes / No / No / No / No
UFS1 / Yes / Yes / No / No / Yes / Yes / No / No / No / No
UFS2 / Yes / Yes / No / No66 / Yes / Yes / No / Yes / ? / No
LFS / Yes / Yes / Yes38 / No / Yes / Yes / No / Yes / No / No
ext2 / Yes / Yes / No / No / Yes / Yes / No / No / Yes65 / No
ext3 / Yes / Yes / Yes 62 / Yes / Yes / Yes / No / No / ? / No
ext4 / Yes / Yes / Yes 62 / Yes / Yes / Yes / No / No / ? / No
ReiserFS / Yes / Yes / Yes 44 / Yes / Yes / Yes / No / No / ? / No
Reiser4 / Yes / Yes / Yes / No / Yes / Yes / No / ? / ? / Yes 50
OCFS / No / Yes / No / No / Yes / Yes / No / No / No / No
OCFS2 / Yes / Yes / Yes / Yes / Yes / Yes / No / No / No / No
XFS / Yes / Yes / No / Yes / Yes 40 / Yes / Yes / No / ? / No
JFS / Yes / Yes / No / Yes / Yes30 / Yes / No / ? / ? / No
QFS / Yes / Yes / No / No / Yes / Yes / No / No / No / No
Be File System / Yes / Yes / No / Yes / Yes / Yes / ? / ? / No / No
NSS / Yes / Yes / ? / Yes / Yes20 / Yes20 / Yes6 / Yes / No / Yes
NWFS / Yes53 / Yes53 / No / No / Yes20 / Yes20 / Yes6 / ? / No / No
ODS-2 / Yes / Yes18 / No / Yes / No / No / Yes / Yes / No / No
ODS-5 / Yes / Yes18 / No / Yes / No / Yes / Yes / Yes / ? / No
UDF / Yes / Yes / Yes38 / Yes38 / Yes / Yes / No / No / Yes / No
VxFS / Yes / Yes / Yes / No / Yes / Yes / Yes / Yes70 / ? / No
Fossil / No / No / No / No / Yes / Yes / Yes / Yes / No / No
ZFS / Yes / Yes / Yes56 / No56 / Yes / Yes / No / Yes / No / No
VMFS2 / Yes / Yes / No / Yes / Yes / Yes / No / No / No / No
VMFS3 / Yes / Yes / No / Yes / Yes / Yes / No / No / No / No
Hard links / Soft links / Block journaling or / Metadata-only journaling / Case-sensitive / Case-preserving / File Change Log / Internal snapshotting/branching / XIP / Filesystem-level encryption

Allocation and layout policies

/ Tail packing / Transparent compression / Block suballocation / Allocate-on-flush / Extents / Variable file block size 41 / Sparse files
DECtape / No / No / No / No / No / No / No
Level-D / No / No / Yes / No / Yes / No / No
V6FS / No / No / No / No / No / No / No
V7FS / No / No / No / No / No / No / No
FAT12 / No / No 51 / No / No / No / No / No
FAT16 / No / No 51 / No / No / No / No / No
FAT32 / No / No / No / No / No / No / No
HPFS / No / No / No / No / Yes / No / No
NTFS / No / Yes / Partial / No / Yes / No / Yes
HFS Plus / No / No / No / No / Yes / No / Yes
FFS / No / No / 8:1 45 / No / No / No / ?
UFS1 / No / No / 8:1 45 / No / No / No / Yes
UFS2 / No / No / 8:1 45 / No / No / Yes / Yes
LFS / No / No / 8:1 45 / No / No / No / Yes
ext2 / No / No 49 / No 47 / No / No / No / Yes
ext3 / No / No / No 47 / No / No / No / Yes
ext4 / No / No / No 47 / Yes / Yes / No / Yes
ReiserFS / Yes / No / Yes 73 / No / No / No / Yes
Reiser4 / Yes / Yes 50 / Yes 73 / Yes / Yes 39 / No / Yes
OCFS / No / No / No / No / Yes / No / ?
OCFS2 / No / No / No / No / Yes / No / Yes
XFS / No / No / No / Yes / Yes / No / Yes
JFS / No / No / Yes / No / Yes / No / Yes
QFS / No / No / Yes / No / No / No / ?
BFS / No / No / No / No / Yes / No / ?
NSS / No / Yes / No / No / Yes / No / ?
NWFS / No / Yes / Yes 42 / No / No / No / ?
ODS-5 / No / No / No / No / Yes / No / ?
VxFS / No / No / ? / No / Yes / No / Yes
UDF / No / No / No / ? 46 / Yes / No / No
Fossil / No / Yes / No / No / No / No / ?
ZFS / Partial 68 / Yes / ? / Yes 67 / No / Yes / ?
VMFS2 / No / No / Yes / No / No / No / Yes
VMFS3 / No / No / Yes / No / No / No / Yes
Tail packing / Transparent compression / Block suballocation / Allocate-on-flush / Extents / Variable file block size 41 / Sparse files

Notes

Note 1: The Mac OS provides two sets of functions to retrieve file names from a HFS Plus volume, one of them returning the full Unicode names, the other shortened names fitting in the older 31 byte limit to accommodate older applications.
Note 2: HFS Plus mandates support for an escape sequence to allow arbitrary Unicode. Users of older software might see the escape sequences instead of the desired characters.
Note 3: Varies wildly according to block size and fragmentation of block allocation groups.
Note 4: For filesystems that have variable allocation unit (block/cluster) sizes, a range of size are given, indicating the maximum volume sizes for the minimum and the maximum possible allocation unit sizes of the filesystem (e.g. 512 bytes and 128KiB for FAT — which is the cluster size range allowed by the on-disk data structures, although some Installable File System drivers and operating systems do not support cluster sizes larger than 32KiB).
Note 5: NTFS access control lists can express essentially any access policy possible using simple POSIX file permissions, but use of a POSIX-like interface is not supported without an add-on such as Services for UNIX or Cygwin.
Note 6: The file change logs, last entry change timestamps, and other filesystem metadata, are all part of the extensive suite of auditing capabilities built into NDS/eDirectory called NSure Audit. (Filesystem Events tracked by NSure)
Note 7: While FAT32 partitions this large work fine once created, some software won't allow creation of FAT32 partitions larger than 32GiB. This includes, notoriously, the Windows XP installation program and the Disk Management console in Windows 2000, XP, 2003 and Vista. Use FDISK from a Windows ME Emergency Boot Disk to avoid. [1]
Note 8: ReiserFS has a theoretical maximum file size of 1EiB, but "page cache limits this to 8 Ti on architectures with 32 bit int"[2]
Note 9: XFS has a limitation under Linux 2.4 of 64TiB file size, but Linux 2.4 only supports a maximum block size of 2TiB. This limitation is not present under IRIX.
Note 10:Microsoft first introduced FAT32 in Windows 95 OSR2 (OEM Service Release 2) and then later in Windows 98. NT-based Windows did not have any support for FAT32 up to Windows NT4; Windows 2000 was the first NT-based Windows OS that received the ability to work with it.
Note 11: IBM introduced JFS with the initial release of AIX Version 3.1 in 1990. This file system now called JFS1. The new JFS (sometimes called JFS2), on which the Linux port was based, was first shipped in OS/2 Warp Server for e-Business in 1999.
Note 12: The on-disk structures have no inherent limit. Particular Installable File System drivers and operating systems may impose limits of their own, however. MS-DOS does not support full pathnames longer than 260 bytes for FAT12 and FAT16. Windows NT does not support full pathnames longer than 32767 bytes for NTFS.
Note 13: This is the limit of the on-disk structures. The HPFS Installable File System driver for OS/2 uses the top 5 bits of the volume sector number for its own use, limiting the volume size that it can handle to 64GiB.
Note 14: The f-node contains a field for a user identifier. This is not used except by OS/2 Warp Server, however.
Note 15: Maximum combined filename/filetype length is 236 bytes; each component has an individual maximum length of 255 byes.
Note 16: Maximum pathname length is 4096 bytes, but quoted limits on individual components add up to 1664 bytes.
Note 17: Record Management Services (RMS) attributes include record type and size, among many others.
Note 18: These are referred to as "aliases".
Note 19: Novell calls this feature "multiple data streams". Published specifications say that NWFS allows for 16 attributes and 10 data streams, and NSS allows for unlimited quantities of both.
Note 20: Case-sensitivity/Preservation depends on client. Windows, DOS, and OS/2 clients don't see/keep case differences, whereas clients accessing via NFS or AFP may.
Note 21: Published specs say that the 128-bit file system provides for up to 264 bytes to describe the file system, file size, directory entries, etc, with a theoretical max of 2128 bytes total to describe all storage on such a machine.
Note 22: Particular Installable File System drivers and operating systems may not support extended attributes on FAT12 and FAT16. The OS/2 and Windows NT filesystem drivers for FAT12 and FAT16 support extended attributes (using a "EADATA.SF" pseudo-file to reserve the clusters allocated to them). Other filesystem drivers for other operating systems do not.
Note 23: Some Installable File System drivers and operating systems may not support extended attributes, access control lists or security labels on these filesystems. Linux kernels prior to 2.6.x may either be missing support for these altogether or require a patch.
Note 24: Depends on whether the FAT12, FAT16, and FAT32 implementation has support for LFNs. Where it does not, as in OS/2, MS-DOS, Windows 95, Windows 98 in DOS-only mode and the Linux "msdos" driver, file names are limited to 11 8-bit characters (space padded in both the basename and extension parts) and may not contain NUL (end-of-directory marker) or character 5 (replacement for character 229 which itself is used as deleted-file marker). Short names also do not normally contain lowercase letters. Also note that a few special names (CON, NUL, LPT1) should be avoided, as some operating systems (notably DOS and windows) effectively reserve them.
Note 25: These are the restrictions imposed by the on-disk directory entry structures themselves. Particular Installable File System drivers may place restrictions of their own on file and directory names; and particular and operating systems may also place restrictions of their own, across all filesystems. MS-DOS, Microsoft Windows, and OS/2 disallow the characters \ / : ? * " > < | and NUL in file and directory names across all filesystems. Unices and Linux disallow the characters / and NUL in file and directory names across all filesystems.
Note 26: In these filesystems the directory entries named "." and ".." have special status. Directory entries with these names are not prohibited, and indeed exist as normal directory entries in the on-disk data structures. However, they are mandatory directory entries, with mandatory values, that are automatically created in each directory when it is created; and directories without them are considered corrupt.
Note 27: The "." and ".." directory entries in HPFS that are seen by applications programs are a partial fiction created by the Installable File System drivers. The on-disk data structure for a directory does not contain entries by those names, but instead contains a special "start" entry. Whilst on-disk directory entries by those names are not physically prohibited, they cannot be created in normal operation, and a directory containing such entries is corrupt.
Note 28: NSS allows files to have multiple names, in separate namespaces.
Note 29: Some file and directory metadata is stored on the NetWare server irrespective of whether Directory Services is installed or not, like date/time of creation, file size, purge status, etc; and some file and directory metadata is stored in NDS/eDirectory, like file/object permissions, ownership, etc.
Note 30: Particular Installable File System drivers and operating systems may not support case sensitivity for JFS. OS/2 does not, and Linux has a mount option for disabling case sensitivity.
Note 31: The local time, timezone/UTC offset, and date are derived from the time settings of the reference/single timesync source in the NDS tree.
Note 32: Some operating systems implemented extended attributes as a layer over UFS1 with a parallel backing file (e.g., FreeBSD 4.x).