HPFS – High Performance File System
The (HPFS) or High Performance File System was developed by Microsoft and Intel for OS/2 1.2, for the most part to support the LAN Manager file server. The tables that describe the location of files and free space are positioned at regular intervals throughout the dataset. New datasets are written where there is a large amount of free space, which reduces fragmentation and keeps the disk arm from jumping around large areas of the disk. HPFS maintains a 512 byte allocation unit no matter how large the volume gets to be.
When Microsoft and Intel created OS/2, they sought to create an operating system that was more capable than the DOS and Windows versions then available. At the time, the only file system widely used on small computers was the FAT file system, which had a number of significant limitations. The FAT file system was restricted in terms of the size of partitions it could support, allowing only 11-character names, no real organization, and no real security and reliability features that are important to individual, business and corporate “power” users. In order to address these concerns, a new file system was created specifically for OS/2, the High Performance File System or HPFS.
HPFS offered many significant improvements over the FAT file system, but also had a few of its own problems. Let’s review the good and the bad:
- OS/2 Native File System.
- Support for long file names (up to 254 characters) and mixed-case file names.
- Directory positioned through the disk.
- Faster file creation.
- More efficient use of disk space, since files are stored on a per-sector basis instead of using multiple-sector clusters. Allocation of individual sectors at 512 bytes.
- Better performance due to overall design, including an internal architecture designed to keep related items closer to each other on the disk volume.
- Less fragmentation of data over time, and less need to defragment the file system.
- Uses more system memory.
The HPFS directory allows file names to be long, to have multiple periods, and to have lowercase letters. Unlike NT and Windows 95, however, HPFS does not maintain separate 8.3 file names for each dataset. If a DOS or Windows program running under OS/2 looks at a directory, it will not see the datasets that have long file names.
HPFS keeps information in a disk cache area of memory until it needs to be written to disk. The problem that this creates is a bit obvious, as a user must insure that all the information has been properly written to disk by shutting the system down by command rather than just turning the power off. If the system suddenly crashes, the data in memory is lost, and the HPFS volume that was in use during the crash is marked “dirty”. Before that volume can be used again, CHKDSK must be run during the very next boot of the operating system in order to examine the chains of free space and file locations to correct any problems. As the disk volumes get larger, the after crash CHKDSK can take an extremely long time.
Its impossible to replicate every possible scenario, however one test sample involved the installation of an application with a large number of files on a FAT disk. After 40 minutes the installation was only 60% complete and had to be terminated. During a second test, the installation was repeated on an HPFS system and completed in 10 minutes. Unfortunately the HPFS code and cache use a significant amount of memory, and the loss of memory can and does effect performance, therefore HPFS is not recommended on small systems with less than 8-16 megabytes of RAM. Obviously this is not an issue in today’s memory loaded systems, but then again you may wonder why you should bother with HPFS anyway!
HPFS is the native file system for OS/2, providing full support for it. At one time, Windows NT supported HPFS, but Microsoft removed this option when NT moved from 3.51 to NT 4.0. You can modify NT and reinstall support for HPFS, and instructions for doing so are freely available on the Internet. Just use your favorite search engine and search for “HPFS NT”. We are informed that there are also drivers for DOS and therefore Windows 95, and Linux has standard installable HPFS drivers
Considering how much more advanced it was than FAT, one might have thought that HPFS would have become quite popular. Unfortunately, HPFS was tied inextricably to OS/2, and for a number of reasons, many of them related to the politics between IBM and Microsoft, OS/2 never really became what it could have been. As interest in OS/2 died, so did support for HPFS. Many of the features of HPFS appear to have been incorporated into NTFS by Microsoft, or at least NTFS has some definite similarities to HPFS.
You can find more information about HPFS by reading this excerpt, Microsoft Systems Journal Sept 1989 v4 n5 p1(13) Full Text © Microsoft Corp. 1989. This excerpted page includes a discussion of the internal architectural characteristics of HPFS volumes.
Notice: Windows® 95, Windows® 98, Windows® NT, Windows® 2000, Windows® XP and Microsoft® Office are registered trademarks or trademarks of the Microsoft Corporation.
All other trademarks are the property of their respective owners.