Well, those are surprising responses for me anyway I guess. 

Here's the thing about special files. They have an integer 'x' attached to them which basically means "this file represents an index into an internal kernel struct'.

Now if you are comfortable with the idea that a file, with a number attached to its metadata, said number representing an index into an array of structs, which has to work for all time and all kernels: then we're just comfortable with different things. 'nuf said. 

moving right along, when did /dev first appear?

On Wed, Feb 7, 2018 at 8:40 AM Nemo <cym224@gmail.com> wrote:
[top-post righted]
> On 2/6/2018 9:06 PM, Dan Cross wrote:
>
> On Tue, Feb 6, 2018 at 8:48 PM, Dave Horsfall <dave@horsfall.org> wrote:
>>
>> On Wed, 7 Feb 2018, Greg 'groggy' Lehey wrote:
>>>>
>>>> V3 and earlier still *called* them special files, but it seems they were
>>>> essentially just magic inode numbers (there was no physical file on disk,
>>>> just any directory entry with the given inode would be the special file).
>>>
>>> Isn't that still the case?
>>
>> Wasn't that "devfs" (which Penguin/OS calls "udev")?  I've never grokked
>> that concept.
>
> No. devfs was (is?) a pseudo-filesystem where only special files
> corresponding to the devices enumerated by the kernel during
> autoconfiguration are present. The contents are synthesized at boot time and
> the filesystem is mounted at some canonical location (like /dev), but is
> otherwise ephemeral. This is in contrast to the older /dev, which is usually
> just a directory on the root filesystem, wherein one created a number of
> device files that may (or may not) correspond to an actual hardware device
> in the system (remember the old dance of, "cd /dev && ./MAKEDEV foo" when
> you added a "foo" onto your system?). The inodes and directory entries for
> those files actually exist in the disk-resident filesystem structures
> (though of course data blocks aren't allocated to those files and the inode
> doesn't refer to any data blocks).
[...]
>         - Dan C.
>
>
On 7 February 2018 at 11:24, Arthur Krewat <krewat@kilonet.net> wrote:
> medusa# mount | egrep '^/dev'
> /devices on /devices read/write/setuid/devices/rstchown/dev=9640000 on Fri
> Jan 19 16:33:07 2018
[...]
> SunOS medusa 5.11 11.3 i86pc i386 i86pc

Further more (5.10 sun4u):

File Systems                                           devfs(7FS)

NAME
     devfs - Devices file system

DESCRIPTION
     The devfs filesystem manages a name  space  of  all  devices
     under  the Solaris operating environment and is mounted dur-
     ing boot on the /devices name space.

     The /devices name space is dynamic and reflects the  current
     state  of  accessible  devices  under  the Solaris operating
     environment. The names of all attached device instances  are
     present under /devices.

     The content under /devices is under the exclusive control of
     the devfs filesystem and cannot be changed.

N.