[TUHS] why does tar have the tape device hard coded into it and why is it mt1 instead of mt0

[clemc@ccc.com (Clem Cole)]

First, the device # should be usable from the command line, i.e.  tar cv0
foo

As for mt, it was written for the tape device and in those days most of us
had at least one 9-track device.    I have no memory of why Ken used mt1
not mt0.   Doug may know.

On Fri, Dec 11, 2015 at 5:27 PM, Will Senn <will.senn at gmail.com> wrote:

> All,
>
> In my exploration of v6, I followed the advice in "Setting up Unix -
> Seventh Edition" and copied v6tar from v7 to v6. Life is good. However, tar
> is using mt1 and it is hard coded into the source, tar.c:
> char    magtape[]       = "/dev/mt1";
>
> As the subject line suggested, I have two questions for those of you who
> might know:
>
> 1. Why is it hard coded?
> 2. Why is it the second device and not the first?
>
> Interestingly, it took me a little while to figure out it was doing this
> because I didn't actually move files between v6 and v7 until today. Before
> this my tests had been limited to separate tests on v6 and v7 along the
> lines of:
>
> cd /wherever
> tar c .
> followed by
> tar t
> list of files
> cd /elsewhere
> tar x
> files extracted and matching
>
> What it was doing was writing to the non-existant /dev/mt1, which it then
> created, tarring up stuff, and exiting. Then when I listed the contents of
> the tarfile, or extracted the contents, it was successful. But, when I went
> to move the tape between v6 and v7, the tape (mt0) was blank, of course. It
> was at this point that I followed  Noel's advice and "Used the source", and
> figured out that it was hard-coded as you see above.
>
> Thanks,
>
> Will
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