Installable File System

from Wikipedia, the free encyclopedia

The Installable File System Framework is an operating system component that allows application programs to only see and handle one file system via a central interface , even if the operating system has to access different file systems via different drivers .

Situation before IFS

There is no such framework in MS-DOS . Application programs use the operating system call INT 21H to use the FAT file system. A driver of another file system must redirect this call to itself, then check whether it is responsible for the processing (i.e. a file is being accessed that is in its file system) and process the call - or (if not responsible) the Pass the call on to the original processing routine. If several such drivers are to be loaded, difficulties can arise:

  • If a driver A considers itself "responsible" for a call without being it, the call usually fails and the actually responsible driver B does not get a chance - the faulty driver A further up the "chain" is not sufficient to call further.
  • If a driver latches on to the beginning of the chain, but (if not responsible) does not forward it at all or does not forward it correctly to subsequent drivers, these are cut off.
  • Hardware-related programs sometimes require that file access means FAT access, and fail if another driver takes over.

Frequent drivers for this file system driver chain are drivers for CD-ROM file systems (including DVD, etc.) as well as " Network Redirector " drivers, which show network resources as local drives.

Introduction of IFS

Under Windows 3.x , the above DOS methodology is possible as well as two network redirectors, one of which must be the "Microsoft Windows Network Redirector".

Only with Microsoft Windows 95 (as well as IBM OS / 2 ) were all file system accesses combined in the Installable File System (IFS) Manager , which can manage any number of drivers for local drives / file systems and network overlays.