Editing Installable File System (section)

===IFS in OS/2===
The IFS provided a basic and powerful interface for programming filesystems.
It was introduced in 1989 in OS/2 1.20, along with the HPFS filesystem.

Filesystem drivers executed in kernel-space ([[ring 0 (computer security)|ring 0]]) and are divided in four principal pieces: microIFS, miniIFS, IFS, helpers.

Only the IFS and the filesystem code itself is required and it is loaded via an "[[IFS (CONFIG.SYS directive)|IFS]]=" statement in the [[CONFIG.SYS]] file.
It is a [[New Executable|NE]] [[16-bit]] [[dynamically loaded library]]. No matter if it is a [[32-bit]] OS/2 (2.0 and newer), the IFS is always 16-bit (although extraofficially you can make a 32-bit IFS).

The microIFS is a piece of code that loads in memory the kernel and the miniIFS and jumps to kernel execution. It is usually in the boot portion of the filesystem.

The miniIFS is a piece of code that is called by the kernel to load the first IFS statement that appears in the CONFIG.SYS file, so the first IFS statement must be the boot's filesystem for the system to be able to boot.

The helpers are 16-bit (for OS/2 1.x) or 32-bit (for OS/2 2.x and up), are executed in user-space ([[Ring 3 (computer security)|ring 3]]) and contain the code used for typical filesystem maintenance, and are called by <code>[[CHKDSK]]</code> and <code>[[disk formatting|FORMAT]]</code> utilities.

This four-piece scheme allowed developers to dynamically add a new bootable filesystem, as the [[ext2]] driver for OS/2 demonstrated.

[[CD-ROM]] filesystem driver ([[ISO 9660]]) was added in OS/2 2.0, [[Universal Disk Format|UDF]] was added in OS/2 4.0 and [[IBM Journaled File System 2 (JFS2)|JFS]] was added in OS/2 4.5.
[[ArcaOS]], the latest packaging of OS/2, has a number of filesystem drivers available, including FAT32.<ref>{{cite web|url=https://www.arcanoae.com/wiki/fat32/|title=FAT32 Installable File System Driver|access-date=2020-09-04}}</ref>
There was also an official 32-bit HPFS IFS, called [[HPFS386]] that improved performance and added some features, like variable size cache and [[Access Control Lists]], and was available only in certain OS/2 server editions.
The FAT filesystem was never removed from the kernel and officially never an IFS, although there are FAT IFS that added features like [[long filename|long file names]] (LFNs), [[FAT32]] support, etc.

Network file-sharing protocols like [[Network File System (protocol)|NFS]] and [[Server Message Block|SMB]] are also implemented using IFS, and the IFS interface never changed.