|Full name||High Performance File System|
|Introduced||November 1989OS/2 1.2with|
|Directory contents||B tree|
|File allocation||B+ tree|
|Max. volume size||64 GiB (as implemented)|
2 TiB (theoretical)
|Max. file size||2 GiB|
|Max. number of files||Unlimited|
|Max. filename length||255 characters|
|Allowed characters in filenames||Single-byte from |
|Dates recorded||Access, Creation, Modified|
|Attributes||Read-only, hidden, system, archive|
|File system permissions||Yes (only in HPFS386)|
|Supported operating systems||OS/2, Windows NT, Linux, DragonFly BSD, eComStation, ArcaOS|
HPFS (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, and released in 1988.
Compared with FAT, HPFS provided a number of additional capabilities:
IBM offers two kinds of IFS drivers for this file system:
HPFS386's cache is limited by the amount of available memory in OS/2's system memory arena and was implemented in 32-bit assembly language. HPFS386 is a ring 0 driver (allowing direct hardware access and direct interaction with the kernel) with built-in SMB networking properties that are usable by various server daemons, whereas HPFS is a ring 3 driver. Thus, HPFS386 is faster than HPFS and highly optimized for server applications. It is also highly tunable by experienced administrators.
Though IBM still had rights to HPFS, its agreement with Microsoft to continue licensing the HPFS386 version was contingent upon the company paying Microsoft a licensing fee for each copy sold. This was a result of the Microsoft and IBM collaboration that gave both the right to use Windows and OS/2 technology.
Windows 95 and its successors Windows 98 and Windows Me can read and write HPFS only when mapped via a network share; they 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 3.51 can also read and write from local HPFS formatted drives. Starting with Windows NT 4 the filesystem driver PINBALL.SYS enabling the read/write access is not shipped anymore. Later Windows versions do not ship with this driver. Note that this driver is limited to 4GB HPFS volumes.
Microsoft retained rights to OS/2 technologies, including the HPFS filesystem, after they ceased collaboration with IBM. 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 the FAT12 and FAT16 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, which simply replays the journal.