Getting the Boot:HPFS

By Howard Gilbert

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 * OS/2 Native File System
 * Supports long file names with mixed case
 * Directory positioned throughout the disk
 * Much faster to create new files
 * Allocates individual sectors (512 bytes)
 * Uses more memory

The High Performance File System (HPFS) was developed by Microsoft for OS/2 1.2, mostly to support the LAN Manager file server. The tables that describe the location of files and freespace are positioned at regular intervals throughout the dataset. New datasets are written where there is a large amount of freespace. This reduces fragmentation and keeps the disk arm from jumping around a large area. HPFS maintains a 512 byte allocation unit no matter how large the volume gets to be.

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 keep a separate 8.3 file name around 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. To be sure that all the information has been properly written to disk, a user should try to shut the system down by command rather than just turning the power off. However, the system will occasionally crash. Any HPFS volume that was in use during a crash is marked "dirty". Before it can be used, the next boot of the operating system must run the CHKDSK utility to examine the chains of freespace and file locations to correct any problems. As the disk volumes get larger, the CHKDSK after a crash can take a very long time.

It is difficult to generalize from individual examples, but the author had the experience of trying to install an application with a large number of files on a FAT disk. After 40 minutes the installation was 60% complete and had to be interrupted. Later on, the installation was repeated on an HPFS system and completed in 10 minutes.

The HPFS code and cache use a significant amount of memory. The loss of memory can effect performance, so HPFS is not recommended on small systems (say with 4-8 megabytes of RAM).

OS/2 regards HPFS as its native file system and provides full support. Windows NT used to support HPFS, but Microsoft removed this option starting with NT 4.0. Instructions are available to modify NT and reinstall support for HPFS. PCLT does not recommend such software, but to find it search www.altavista.digital.com for "HPFS NT" and look around.

There are also drivers for DOS and therefore Windows 95. Linux has standard installable HPFS drivers.

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