9 Mar
2017
9 Mar
'17
10:10 a.m.
http://museo.freaknet.org/en/recupero-dati-nastri-magnetici-del-computer-po…
--
Liam Proven ? Profile: https://about.me/liamproven
Email: lproven at cix.co.uk ? Google Mail/Talk/Plus: lproven at gmail.com
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UK: +44 7939-087884 ? ?R/WhatsApp/Telegram/Signal: +420 702 829 053
10 Mar
10 Mar
12:59 p.m.
This is fsckin cool.
Chuck and I were wondering how it turned out.
On 3/9/17 7:10 AM, Liam Proven via cctalk wrote:
1:16 p.m.
On 03/10/2017 09:59 AM, Al Kossow via cctalk wrote:
This is fsckin cool. Chuck and I were wondering how it
turned out.
On 3/9/17 7:10 AM, Liam Proven via cctalk wrote:
>
http://museo.freaknet.org/en/recupero-dati-nastri-magnetici-del-computer-po…
That's pretty amazing, considering the crappy nature of those Qualstar
drives.
I may give it a try.
--Chuck
1:19 p.m.
Spinning at 50ips probably helped instead of the default 20
I would have digitized the tach signal too, but luckily it wasn't needed
Sad neither you or I are mentioned in the credits
I'm going to try it as well, since I have all the hw to try it out.
On 3/10/17 10:16 AM, Chuck Guzis via cctalk wrote:
On 03/10/2017 09:59 AM, Al Kossow via cctalk wrote:
This is fsckin cool. Chuck and I were wondering
how it turned out.
On 3/9/17 7:10 AM, Liam Proven via cctalk wrote:
>
http://museo.freaknet.org/en/recupero-dati-nastri-magnetici-del-computer-po…
That's pretty amazing, considering the crappy nature of those Qualstar
drives.
I may give it a try.
--Chuck
1:22 p.m.
On Mar 9, 2017, at 10:10 AM, Liam Proven via cctalk
<cctalk at classiccmp.org> wrote:
http://museo.freaknet.org/en/recupero-dati-nastri-magnetici-del-computer-po…
Neat.
The software mentioned in the article sounds very interesting. It talks about starting
with digital data streams from the 9 heads, but adds that you can start with analog data
too. That would be a small change: you'd basically have to add the slicer in
software. That's potentially valuable, if the signals are marginal so the threshold
needs to adjust on the fly.
Obviously this can also be adapted to other tape formats, for example 7 track tapes. Or
esoteric stuff like 10 track tapes.
Thanks for that link!
paul
1:39 p.m.
The next extension is to track the tachometer values so that you can detect and compensate
for tape stick/drag
which is absolutely critical for formats that don't self-clock, like NRZI.
Fortunately, they mention that the tapes they worked with were in good condition.
The killer problem with the Qualstar is the reel motors are low torque. If you get a
sticky tape, the RPMs go wonky.
Good news is the Saleae 16 can do digital and analog capture.
On 3/10/17 10:22 AM, Paul Koning via cctalk wrote:
The software mentioned in the article sounds very
interesting. It talks about starting with digital data streams from the 9 heads, but adds
that you can start with analog data too. That would be a small change: you'd
basically have to add the slicer in software. That's potentially valuable, if the
signals are marginal so the threshold needs to adjust on the fly.
Obviously this can also be adapted to other tape formats, for example 7 track tapes. Or
esoteric stuff like 10 track tapes.
Thanks for that link!
paul
1:58 p.m.
On Mar 10, 2017, at 1:39 PM, Al Kossow via cctalk
<cctalk at classiccmp.org> wrote:
The next extension is to track the tachometer values so that you can detect and
compensate for tape stick/drag
which is absolutely critical for formats that don't self-clock, like NRZI.
NRZI is not self clocking if you consider an individual track in isolation. But it IS if
you consider all the tracks at the same time, provided either (a) the data is recorded
with odd parity, or (b) the all-zeroes data character isn't used. (a) is the case for
9-track tapes. 7 track tapes may be even parity, but that case seems to apply by
convention only to text data (not binary data) and there, (b) applies. You do have to
correct for track skew in this process, but that applies in any case even if you have an
independent authoritative bit clock.
It clearly can help to have tach signals as a way to improve bit framing, but I don't
see that it's mandatory.
paul
2:25 p.m.
On 03/10/2017 10:58 AM, Paul Koning via cctalk wrote:
I think I mentioned that a couple of years ago. Even parity 7 track
tapes were used on very old systems for reasons that escape me. One of
the problems, then was how to represent an all-zero character, since
there would be no transitions in that particular frame.
A tach signal is useful for adjusting the width of the "window" when
deskewing.
I wonder if there's not a better way to attack the problem with some
simple hardware. The original posters mentioned an AVR Arduino as
their initial platform, but cheap SBCs are available that run much, much
faster. Consider, for example, the RPi zero or the Orange Pi zero or a
host other sub-$10 hosts running at a GHz or more.
You'd need level-shifting for a modern MCU/CPU anyway, as logic levels
are most commonly 3.3V, not 5V.
--Chuck
On Mar 10, 2017, at 1:39 PM, Al Kossow via
cctalk
<cctalk at classiccmp.org> wrote:
The next extension is to track the tachometer values so that you
can detect and compensate for tape stick/drag which is absolutely
critical for formats that don't self-clock, like NRZI.
NRZI is not self clocking if you consider an individual track in
isolation. But it IS if you consider all the tracks at the same
time, provided either (a) the data is recorded with odd parity, or
(b) the all-zeroes data character isn't used. (a) is the case for
9-track tapes. 7 track tapes may be even parity, but that case seems
to apply by convention only to text data (not binary data) and there,
(b) applies. You do have to correct for track skew in this process,
but that applies in any case even if you have an independent
authoritative bit clock.
It clearly can help to have tach signals as a way to improve bit
framing, but I don't see that it's mandatory.
2:40 p.m.
On Mar 10, 2017, at 2:25 PM, Chuck Guzis via cctalk
<cctalk at classiccmp.org> wrote:
On 03/10/2017 10:58 AM, Paul Koning via cctalk wrote:
I think I mentioned that a couple of years ago. Even parity 7 track
tapes were used on very old systems for reasons that escape me. One of
the problems, then was how to represent an all-zero character, since
there would be no transitions in that particular frame.
Sure. One tape document I looked at mentions the use of odd parity on the 7-track tapes
when writing binary data, even parity when writing "IBM BCD" character coded
data, with one of the 6-bit values forbidden in that case (the value encoded on tape as 6
zero bits).
A stretch with no transitions occurs of course at the block boundary (the gap). It also
apparently occurs in other spots, for a few bit times: tape marks seem to consist of two
frames separated by a few clocks worth of blank space. Ditto between data and block check
frame(s), if I remember right.
On Mar 10, 2017, at 1:39 PM, Al Kossow via
cctalk
<cctalk at classiccmp.org> wrote:
The next extension is to track the tachometer values so that you
can detect and compensate for tape stick/drag which is absolutely
critical for formats that don't self-clock, like NRZI.
NRZI is not self clocking if you consider an individual track in
isolation. But it IS if you consider all the tracks at the same
time, provided either (a) the data is recorded with odd parity, or
(b) the all-zeroes data character isn't used. (a) is the case for
9-track tapes. 7 track tapes may be even parity, but that case seems
to apply by convention only to text data (not binary data) and there,
(b) applies. You do have to correct for track skew in this process,
but that applies in any case even if you have an independent
authoritative bit clock.
It clearly can help to have tach signals as a way to improve bit
framing, but I don't see that it's mandatory. A tach signal is useful for adjusting the width of the
"window" when
deskewing.
Yes, that was my point: useful to make the process easier or to improve the quality of the
result if the inputs are marginal, but you can make it work without a tach signal.
I wonder if there's not a better way to attack the
problem with some
simple hardware. The original posters mentioned an AVR Arduino as
their initial platform, but cheap SBCs are available that run much, much
faster. Consider, for example, the RPi zero or the Orange Pi zero or a
host other sub-$10 hosts running at a GHz or more.
You'd need level-shifting for a modern MCU/CPU anyway, as logic levels
are most commonly 3.3V, not 5V.
Al's mention of that Saleae device fits there: you could plug that into any suitable
fast enough computer, and it deals with analog data so you can do the threshold in
software. (Thanks Al, those look like nice devices.)
paul
9:47 p.m.
On 03/10/2017 01:40 PM, Paul Koning via cctalk wrote:
A stretch with no transitions occurs of course at the
block boundary (the gap). It also apparently occurs in
other spots, for a few bit times: tape marks seem to
consist of two frames separated by a few clocks worth of
blank space. Ditto between data and block check frame(s),
if I remember right.
The classic NRZI definition for 800 BPI 9-track is that
there is a 2-character gap after the end of the user data
block, then the CRC and LRCC characters follow. We had some
tapes made on out IBM 360 that had little short gaps all
over them, as they had the machine misconfigured and were
exceeding memory bandwidth. The IBM could read them fine.
I think they only detected the big gap to define the end of
the record. Our DEC controllers all used the 2-character
gap to detect where the block was ending. No way to fix
that if the hardware tape control decided those gaps were
the end of data.
Jon
9:42 p.m.
On 03/10/2017 12:58 PM, Paul Koning via cctalk wrote:
Yes, but the problem is 800 BPI is about the upper limit on
density due to tape skew. I don't know for sure, but I
strongly suspect that skew gets worse as the tape gets
older. I've seen some tapes that were only a few years old
where the skew got very bad. You could put a scope on the
skew alignment test point and see the skew pattern pulsing
as the supply reel rotated, meaning the tape got
differentially stretched while sitting on the reel.
But, glad they were so successful in their effort!
Jon
On Mar 10,
2017, at 1:39 PM, Al Kossow via cctalk <cctalk at classiccmp.org> wrote:
The next extension is to track the tachometer values so that you can detect and
compensate for tape stick/drag
which is absolutely critical for formats that don't self-clock, like NRZI.
NRZI is not self clocking if you consider an individual track in isolation. But it IS if
you consider all the tracks at the same time, provided either (a) the data is recorded
with odd parity, or (b) the all-zeroes data character isn't used. (a) is the case for
9-track tapes.
2694
days inactive
2696
days old
10 comments
5 participants
participants (5)
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aek＠bitsavers.org -
cclist＠sydex.com -
elson＠pico-systems.com -
lproven＠gmail.com -
paulkoning＠comcast.net