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An extensible system is one that enables extensibility.  Enabling extensibility
means providing non-privileged mechanisms to extend existing objects and to
introduce new objects.  [[UNIX]] is generally not an extensible system as it does
not generally facilitate the hooking of [[system call]]s.  For instance, there is
no way to hook into the virtual file system.  This has motivated the introduction
of separate, parallel interfaces by both the GNOME and KDE projects to provide
users a more integrated view of their objects.

The Hurd introduces the concept of [[translators|hurd/translator]] to let users 
hook into the virtual filesystem.  We have translators that let ordinary users 
create their own [[ext2 filesystem|hurd/translator/ext2fs]], 
[[ftp filesystem|hurd/translator/ftpfs]], iso filesystem, 
[[http filesystem|hurd/translator/httpfs]], etc.  You can get started using
the existing translators by reading the [[how to|hurd/translator/examples]] page.

The Hurd's extensibility is not just limited to the VFS.  It is possible for
users to have their own [[TCP/IP|hurd/translator/pfinet]] 
[[stack|hurd/translator/lwip]] using the [[hurd/translator/remap]]
translator.  Users can create their own 
[[personal firewall|https://darnassus.sceen.net/~hurd-web/hurd/translator/eth-filter/]],
run a personal [[hurd/translator/auth]] server, or isolate untrusted applications inside
a [[hurd/subhurd]].  The possibilities are endless!

# External
* The Wikipedia article on [[!wikipedia extensibility]]