Ok, the story so far. Berny wrote: Here's the breakdown of SVR4 kernel lineage as I recall it. ... From SunOS: vnodes VFS Dan Cross wrote: Surely Berny meant the file system switch here, which could have come from early system V, but originated in research Unix (8th edition?). Joerg Schilling wrote: It is rather a part of the VFS interface that has first been completed with SunOS-3.0 in late 1985. And this is where the confusion starts. Does "It" refer to FSS or VFS? I've just looked through some sources. The file system switch was in SysVR3: uts/3b2/sys/mount.h: /* Flag bits passed to the mount system call */ #define MS_RDONLY 0x1 /* read only bit */ #define MS_FSS 0x2 /* FSS (4-argument) mount */ VFS was in SunOS 4.1.4: sys/sys/vfs.h: struct vfssw { char *vsw_name; /* type name string */ struct vfsops *vsw_ops; /* filesystem operations vector */ }; And VFS is in SysVR4: uts/i386/sys/vfs.h: typedef struct vfssw { char *vsw_name; /* type name string */ int (*vsw_init)(); /* init routine */ struct vfsops *vsw_vfsops; /* filesystem operations vector */ long vsw_flag; /* flags */ } vfssw_t; Interestingly, the "filesystem operations vector" comment also occurs in FreeBSD 5.3, NetBSD-5.0.2 and OpenBSD-4.6. Look for vector here: http://minnie.tuhs.org/cgi-bin/utree.pl?file=FreeBSD-5.3/sys/sys/mount.h http://minnie.tuhs.org/cgi-bin/utree.pl?file=NetBSD-5.0.2/sys/compat/sys/mo… http://minnie.tuhs.org/cgi-bin/utree.pl?file=OpenBSD-4.6/sys/sys/mount.h Larry wrote: System Vr3 had something called the file system switch which is what Berny is talking about. SunOS had virtual file system layer (VFS) and that would be one of things ported to SVr4. which is consistent with everybody else. So now that we have consistency, let's move on. Cheers, Warren