Editing High Performance File System (section)

== Overview ==
Compared with FAT, HPFS provided a number of additional capabilities:
*Support for [[Case Sensitivity|mixed case]] file names, in different [[code page]]s
*Support for long file names (255 characters as opposed to FAT's [[8.3]] naming scheme)
*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 [[file system fragmentation|fragmentation]] of data
*[[Extent (file systems)|Extent]]-based space allocation
*Separate datestamps for last modification, last access, and creation (as opposed to last-modification-only datestamp in then-times implementations of FAT)
*[[B+ tree]] structure for directories
*Root directory located at the midpoint, rather than at the beginning of the disk, for faster average access

HPFS also can keep 64 [[Kilobyte|KB]] of [[Metadata (computing)|metadata]] ("[[extended attribute]]s") per file.

IBM offers two kinds of [[Installable File System|IFS]] drivers for this file system:

*The standard one with a cache limited to 2&nbsp;MB
*''HPFS386'' provided with certain server versions of OS/2, or as added component for the server versions that did not come with it

HPFS386's cache is limited by the amount of available memory in OS/2's system memory arena<ref>{{cite web|title=Virtual Memory Problems under OS/2|url=http://www.os2voice.org/VNL/past_issues/VNL0708H/feature_3.html|publisher=www.os2voice.org|access-date=11 June 2015|archive-url=https://web.archive.org/web/20150924061927/http://www.os2voice.org/VNL/past_issues/VNL0708H/feature_3.html|archive-date=24 September 2015|url-status=dead}}</ref> and was implemented in 32-bit [[assembly language]]. HPFS386 is a [[Ring (computer security)|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 [[daemon (computing)|daemon]]s, whereas HPFS is a [[Ring 3 (computer security)|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.

Due to the Microsoft dependence, limited partition size, file size limit of 2&nbsp;GB and the long disk-check times after a crash, IBM ported the [[journaling file system]], [[JFS (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.