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

Clem Cole clemc at ccc.com
Sun Dec 13 06:13:33 AEST 2015

Interesting  memories ... IIRC: workstations were really what caused /dev/*mt*
to stop being a standard name, so not screwing it down and using the -f
option made sense. But for a long time, since it was less typing on the 11s
and Vaxen, I would do:
           tar cvb0 20 mumble...
However, once we moved to the world of networking, the -f option became
important to me.
*i.e. *   tar cvf - mumble | rmt hosts ...

Also, the DEC drives had better buffering.  Large buffers became really
important with streaming versions of 9-track and of course for the later
QIC tapes.  So blocking became even more important and I quit doing that
function with tar itself and started to pipe tar through dd to do the
blocking to get really large blocks (like 256K or 1M).   Also, tools
appeared like "double dd" (aka ddd(1)) program that originally used a two
processes and pipe to coordinates the writes so that we could stream a
Cipher drive on a 10Mhz 68K (Masscomp box).

[Note to Will - you might to google for the original ddd or talk to me
offline, I bet I have it somewhere.  Its an interesting program to analyze
if you really want to get some insight on what you could do with UNIX even
on a "slow" computer by today's standards and without a lot of today's
fancy API's].

tjt rewrote dump(1) on RTU to use AST's and may have hacked dd too (I've
lost that version I fear).  In the mid, 80's I rewrote ddd to use threads
once kernel support for threading became available and I still use that
version today when I mess with tapes (which I do less and less, but have
been known to do when trying to recover old tapes).


On Sat, Dec 12, 2015 at 1:54 PM, Mary Ann Horton <mah at mhorton.net> wrote:

> Yeah, I just can't imagine using tar with the f option.  Even back in the
> day when I was writing 9 track magtapes with tar, it would be something like
>     tar cvfb /dev/rmt0 10 .
> to get tape blocks bigger than 512 bytes.  But we never had dectapes and I
> think they did their own blocking.
>     Mary Ann
> On 12/11/2015 06:09 PM, Doug McIlroy wrote:
>> I have no memory of why Ken used mt1 not mt0.   Doug may know.
>> I don't know either. Come to think of it, I can't remember ever
>> using tar without option -f. Direct machine-to-machine trasfer,
>> e.g. by uucp, took a lot of business away from magtape soon
>> after tar was introduced. Incidentally, I think tar was written
>> by Chuck Haley or Greg Chesson, not Ken.
>> Doug
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