installable file system
(IFS or "File System Driver", "FSD") An API that allows you to extend OS/2 to access files stored on disk in formats other than FAT and HPFS, and access files that are stored on a network file server.
The other variety of IFS (a "remote file system" or "redirector") allows file sharing over a LAN, e.g. using Unix's Network File System protocol. In this case, the IFS passes a program's file access requests to a remote file server, possibly also translating between different file attributes used by OS/2 and the remote system.
An IFS is structured as an ordinary 16-bit DLL with entry points for opening, closing, reading, and writing files, the swapper, file locking, and Universal Naming Convention. The main part of an IFS that runs in ring 0 is called by the OS/2 kernel in the context of the caller's process and thread. The other part that runs in ring 3 is a utility library with entry points for FORMAT, RECOVER, SYS, and CHKDSK.