On 2014-05-15 23:10, Clem Cole wrote:
I wrote one of these a long time ago for Tru64, but I do not think I
still have it. The concept is easy:
http://simh.trailing-edge.com/docs/simh_magtape.pdf
Right. Conceptually it is very simple to write a tape image to a
physical tape, as long as the tape image contains the necessary information.
But the problem is it becomes extremely driver specific. You need to
know what marks the driver is going to write for you - which is highly
OS dependent - as well as what the devices does behind the scenes which
is highly device dependent. I was going to 9-track and I know the
details for all of that, but I have not idea how TKxx wrotes tape marks
(I always avoided them as a "bad idea").
Well, there are only one kind of tape marks, and it's not usually any
different for different drivers, but exactly how you write a tape mark
is absolutely OS-dependant.
So any program for Tru64 is essentially useless for someone running VMS
(for example).
In 9-track world, the end of each file is mark as a single meta record
(tape mark), Two in the row marks end-of-tape. So the when you write
a take the driver check to see if its at start of tape and if not, has
to backs up over the last tape mark and then start writing. On close it
writes 2 tape marks.
The two tape marks for logical EOT is a convention, and not all software
adhere to it. But in general, right. I think someone else mentioned it,
but it's worth pointing out that for ANSI labelled tapes, the tape marks
are not used this way, for example.
QIC tapes do not work that way. Exabyte and DAT are closer to 9-track
in rules, but I've forgotten most of the details and I do remember there
was something funky about the original DECtape but those bits in my
brain have long rotted away. You really should open the driver for the
TK50 and see if you can grok it. Look at the open and close code very
carefully.
I don't remember exactly how QIC tapes work, but it rings a bell that
they might have been different.
DECtapes are not tapes in this sense, and so they should be totally left
out of this discussion. DECtapes work the same way a floppy do, but
slower. Fixed length blocks, block addressable, and you can rewrite
individual blocks. There are no tape marks in the way a 9-track have them.
A TK50 works the same way as a 9-track. So do Exabyte, DAT, DDS, DLT,
and any "modern" tape technology of today that I can recall.
Johnny
Clem
On Thu, May 15, 2014 at 4:38 PM, Cory Smelosky <[email protected]
<mailto:[email protected]>> wrote:
Hello all,
Googling around only seems to want to show me how to copy real tapes
to images. I need to copy a SIMH tape image to a real tape!
I seem to recall SIMH including a utility for this...but I could be
mistaken.
I will need a utility that will run on VMS (VAX) as I need to use a
TK50 to make a TK50. (Unless someone wants to doante a TK70. ;) )
--
Cory Smelosky
http://gewt.net Personal stuff
http://gimme-sympathy.org Projects
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