Good point.
About 15-20 years ago we transferred our library (100's, maybe over
1000) of 9-track tapes to a disk archive. I think we sent the tapes
out to be cooked, which was to make sure the adhesive bonding the
oxide coating to the mylar tape was good. I also remember the person
who played back the tapes running them through a tape cleaning machine
before playing them back.
I neglected to mention that, out of the eight tapes I tried to read
last week, one kept getting stuck on the read head. We have a
streaming tape drive now, and it is good at stopping right away when
that happens. I have never had this happen before. I cleaned the
tape surface with alcohol, but that did not help. There must also be
some sort of lubrication in the oxide on 9-track tapes that is no
longer effective on this tape. It was a different brand than the
other tapes, perhaps inferior. I remember in the old days there were
tape head cleaning fluids. I assumed they were just alcohol. Now I
wonder if perhaps they also included a lubricant.
Larry Baker
US Geological Survey
650-329-5608
[email protected]
On 31 Jul 2011, at 5:35 AM, Göran Åhling wrote:
Hi!
Great explanation!
But, a slightly touching question: did you ever have any deeper
thought upon mechanically reading this old tape?
I've just been asked to advice someone that has a unique 1/2"-tape
with measurements data that now suddenly has been of interest to
read out and compare to modern measurements. Format etc would be of
no problem (VMS / RMS is part of the writing...).
The one who asked had heard about old tapes loosing the magnetic
part from the tape film during first unwinding to let it pass the
reading-head of a tape-station. He was speaking from that some
people are said to be talking about "steam-treating" the tapes
before letting the tape out, for example.
Any advice or still better, knowledge, would be greatly appreciated.
/Göran Åhling.
On 2011-07-29 01:44, Larry Baker wrote:
I thought I would pass along something I just discovered about an
old tar tape from 1987.
One of our scientists brought me a stack of old 9-track tapes
(circa 1987-1990) to read this afternoon. All but one were ANSI-
labelled "VAX COPY" tapes. The one that was not said it was a Unix
tar tape. I have a tape scanning program that told me it had a
single file on the tape with 10240 byte blocks, which matches what
you should see on a tar tape. I read it on to our MicroVAX as a
foreign tape with RECORDSIZE=BLOCKSIZE=10240. But, when I tried
to use tar to read it (VMSTAR on our Alpha, tar on my Mac, tar on a
Solaris SPARC workstation), it kept saying it was not a tar
archive. I opened the file on my Mac using TextWrangler. There
were lines that looked like data, and text that looked like it
could be a file name, but I didn't recognize any of the text. I
figured at least it was an uncompressed/unencrypted archive of some
sort (thank goodness). I thought it might be the old Unix dump
tape format, but I could not find out what that format was like (I
didn't spend much time Google searching). I looked once more at
the ASCII in the archive, and mentally byte-swapped some of the
strings that looked like they should have been file names. BINGO!
What looked like gibberish became words. I used dd conv=swab on my
Mac to byte-swap the file and, lo and behold, tar -tf worked.
About the time the tape was written, we had a pair of VAX-11/750's
networked to a VAX-11/785. One of the VAX-11/750's ran BSD Unix.
I don't know whether there was a device name option to select byte-
swapping (in those days, at least, Unix used different device names
for the same tape drive to select among the capabilities of the
device, such as to select the density) or if BSD always byte-
swapped when writing tapes on a VAX (I doubt it -- this is the
first time I have ever encountered a byte-swapped 9-track tape).
Whatever the reason, I thought it might be useful for this group to
know that such tapes exist. Thus, if you get a real tape of a tape
image that purports to be in tar format, but is not, don't give up
-- it could be byte-swapped!
Larry Baker
US Geological Survey
650-329-5608
[email protected]
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