High Performance File System

infobox filesystem
name = HPFS
full_name = High Performance File System
developer = Microsoft
introduction_os = OS/2 1.2
introduction_date = November 1989
partition_id = 0x07 (MBR)
directory_struct = B+ tree
file_struct = B+ tree
bad_blocks_struct = B+ tree
max_filename_size = 256 characters
max_files_no = Unlimited
max_volume_size = 2 TiB | max_file_size = 2 GiB
filename_character_set = Double-byte from 0x0020 to 0xFFFF
dates_recorded = Access, Creation, Modified
date_range =
date_resolution =
forks_streams = Yes
attributes = Read-only, hidden, system, archive
file_system_permissions = Yes (only in HPFS386)
compression = No
encryption = No
OS = OS/2, Windows NT, Linux, FreeBSD

HPFS or High Performance File System is a file system created specifically for the OS/2 operating system to improve upon the limitations of the FAT file system. It was written by Gordon Letwin and others at Microsoft and added to OS/2 version 1.2, at that time still a joint undertaking of Microsoft and IBM.

Among its improvements are:

*support for mixed case file names, in different code pages
*support for long file names (256 characters as opposed to FAT's 8+3 characters)
*more efficient use of disk space (files are not stored using multiple-sector clusters but on a per-sector basis)
*an internal architecture that keeps related items close to each other on the disk volume
*less fragmentation of data
*extent-based space allocation
*separate datestamps for last modification, last access, and creation (as opposed to FAT's one last modification datestamp)
*a B+ tree structure for directories
*root directory located at the mid-point, rather than beginning of the disk, for faster average access

HPFS also can keep 64 KiB of metadata ("extended attributes") per file.

IBM offers two kind of IFS drivers for this file system:

*the standard one with a cache limited to 2 MiB
*HPFS386 provided with the server versions of OS/2

HPFS386's cache is limited by the available memory and was implemented in assembler. Thus, HPFS386 is faster, but IBM is required to pay Microsoft for each copy sold. It is highly tunable by experienced administrators.

IBM had still had right over HPFS , but not HPFS386.This was a result from the Microsoft and IBM collaboration that both IBM and Microsoft had right to use Windows and OS/2 technology. Microsoft used HPFS in Windows NT.

Because of the Microsoft dependence and the long disk check times after a crash, IBM ported the journaling file system JFS to OS/2 as a substitute.

DOS and Linux support HPFS via third-party drivers. Windows NT versions 3.51 and earlier had native support for HPFS.

Windows Native Support

Windows 95 and its successors Windows 98, Windows Me can read/write HPFS only when mapped via a network share, but cannot read it from a local disk. They listed the NTFS partitions of networked computers as "HPFS", because NTFS and HPFS share the same filesystem identification number in the partition table.

Windows NT 3.1 and 3.5 have native read/write support for local disks and can even be installed onto an HPFS partition. This is because NT was originally going to be a version of OS/2.

Windows NT 3.51 can also read and write from local HPFS formatted drives. However, Microsoft discouraged using HPFS in Windows NT 4 and in subsequent versions. Microsoft even removed the ability of NT 3.51 to format an HPFS file system. Starting with Windows NT 4 the filesystem driver pinball.sys enabling the read/write access is not included in a default installation anymore. Pinball.sys is included on the installation media for Windows 2000 and can be manually installed and used with some limitations.Fact|date=March 2007 Later Windows versions do not ship with this driver.

Microsoft retained rights to OS/2 technologies, including the HPFS filesystem after they ceased collaboration. Since Windows NT 3.1 was designed for more rigorous (enterprise-class) use than previous versions of Windows, it included support for HPFS (and NTFS) giving it a larger storage capacity than FAT filesystems. However, since HPFS lacks a journal, any recovery after an unexpected shutdown or other error state takes progressively longer as the filesystem grows. A utility such as CHKDSK would need to scan each entry in the filesystem to ensure no errors are present, a problem which is vastly reduced on NTFS where the journal is simply replayed or rolled back.

See also

* Comparison of file systems

Further reading

* cite journal
url = http://www.2ka.mipt.ru/~alexp/docs/programming/formats/hpfs.pdf
title=Design goals and implementation of the new High Performance File System
author=Roy Duncan
journal=Microsoft Systems Journal
month=September | year=1989|volume=4:5
pages=1–13
* cite news
url=http://www.nondot.org/sabre/os/files/FileSystems/HPFS/
title=Inside the High Performance File System
first=Dan
last=Bridges
publisher=Significant Bits magazine
year=1996
* cite journal
url = http://www.heise.de/ct/97/01/306/
title=HPFS unter Windows NT 4.0
author=Dieter Brors
journal=c't Magazin für Computertechnik (German)
year=1997|volume=1
pages=306
* cite web
url = http://www.warpspeed.com.au./Products/OS2/GU/Manual/appg.htm
title=Appendix G — HPFS internals
author=Chris Graham
work=The Graham Utilities for OS/2 - Version 2
* [http://homepage2.nifty.com/bayer/hpfs_w2k.html#English How to get Windows NT 4, Windows 2000, and Windows XP to read HPFS partitions]