12 Nov
2015
12 Nov
'15
8:24 a.m.
I've had very mixed (about 50/50) success with 9-track, but after reading a
bit about DECtape it looks like they should still be holding up nicely.
Anyone care to share their experiences?
12 Nov
12 Nov
8:47 a.m.
On 2015-11-12 14:24, Tom Moss wrote:
I've had very mixed (about 50/50) success with
9-track, but after reading a
bit about DECtape it looks like they should still be holding up nicely.
Anyone care to share their experiences?
Not sure what there is to share. I've yet to encounter a DECtape I
couldn't read.
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt at softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
10:48 a.m.
On Nov 12, 2015, at 8:47 AM, Johnny Billquist <bqt
at update.uu.se> wrote:
On 2015-11-12 14:24, Tom Moss wrote:
You're right, DECtape is extremely reliable. That makes sense: the tape is a
sandwich, with the oxide underneath a mylar cover.
My boss in college (a former and subsequent DEC OS developer) told me the same thing you
did, that he'd never seen a DECtape fail. Not even the one that was accidentally
laundered (in some pants pockets), or the one that came loose from the hub and rolled all
over the sawdust covered floor of the DEC mill building.
But I told him that I had seen some fail, and he saw it too. This was in college. We had
an early RSTS system where DECtapes were used as public storage (to supplement the RK05
system disk). Those were so busy that they did eventually wear out. Sometimes they could
be reformatted to bring them back to life, sometimes not.
And yes, between the redundant tracks and the physical construction of the tape, you
should expect DECtapes to be perfectly readable even today.
paul
I've had very mixed (about 50/50) success
with 9-track, but after reading a
bit about DECtape it looks like they should still be holding up nicely.
Anyone care to share their experiences?
Not sure what there is to share. I've yet to encounter a DECtape I couldn't read.
10:27 a.m.
On 11/12/2015 07:24 AM, Tom Moss wrote:
I've had very mixed (about 50/50) success with
9-track, but after reading a
bit about DECtape it looks like they should still be holding up nicely.
Anyone care to share their experiences?
Some guys at Washington University restored a LINC that had
been stored in somebody's garage for decades. They mostly
just had to reform the power supply capacitors. Then, they
got some LAP-6 tapes that had been in somebody's office and
it booted right up! These were tapes that likely had been
sitting for 30 years.
LINCtape is essentially identical to DECtape. I think the
directory format is different, but I think the block format
is the same. I think the tapes are wound in reverse order
and the order of increasing block numbers is reversed.
Jon
1:49 p.m.
On 11/12/15 7:27 AM, Jon Elson wrote:
LINCtape is essentially identical to DECtape. I think
the directory
format is different, but I think the block format is the same. I think
the tapes are wound in reverse order and the order of increasing block
numbers is reversed.
Actually the block format is different. "Obverse Compliment" encoding
was created for DECtape. LINCtape blocks aren't bidirectional.
The actual spec for the 3M tape can be found at
http://bitsavers.org/pdf/dec/dectape/3M_DECtape_Spec_nov66.pdf
The protective overlay is .04 mils.
4:29 p.m.
On 2015-11-12 19:49, Al Kossow wrote:
On 11/12/15 7:27 AM, Jon Elson wrote:
Aha. Interesting. I didn't know that the bit patterns of the control
channel was different.
Curious question then - could most DECtape controllers even read LINCtpae?
I know the TD8E can. The most stupid controller on the planet, but it
enables you to deal with just about any DECtape format you could
possibly ever invent.
But other DECtape controllers might not be able to deal with tapes that
use other codes to indicate what is being read...?
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt at softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
LINCtape is essentially identical to DECtape. I
think the directory
format is different, but I think the block format is the same. I think
the tapes are wound in reverse order and the order of increasing block
numbers is reversed.
Actually the block format is different. "Obverse Compliment" encoding
was created for DECtape. LINCtape blocks aren't bidirectional.
4:42 p.m.
On Nov 12, 2015, at 4:29 PM, Johnny Billquist <bqt
at Update.UU.SE> wrote:
On 2015-11-12 19:49, Al Kossow wrote:
I believe you can do this on the TC11 with the READ-ALL operation, but my memory is vague
and the manuals I have handy aren't detailed enough.
paul
On 11/12/15 7:27 AM, Jon Elson wrote:
Aha. Interesting. I didn't know that the bit patterns of the control channel was
different.
Curious question then - could most DECtape controllers even read LINCtpae?
I know the TD8E can. The most stupid controller on the planet, but it enables you to deal
with just about any DECtape format you could possibly ever invent.
But other DECtape controllers might not be able to deal with tapes that use other codes
to indicate what is being read...? LINCtape is essentially identical to DECtape. I
think the directory
format is different, but I think the block format is the same. I think
the tapes are wound in reverse order and the order of increasing block
numbers is reversed.
Actually the block format is different. "Obverse Compliment" encoding
was created for DECtape. LINCtape blocks aren't bidirectional. 
6:27 p.m.
PIP10 will let you read (and ISTR, write) PDP-10 formatted tapes on a
PDP-8/TC08. Been there, done that. I don't know if there would be a
problem on a TD8E setup. -- Ian
On Thu, Nov 12, 2015 at 1:42 PM, Paul Koning <paulkoning at comcast.net> wrote:
--
Ian S. King, MSIS, MSCS, Ph.D. Candidate
The Information School <http://ischool.uw.edu>
Dissertation: "Why the Conversation Mattered: Constructing a Sociotechnical
Narrative Through a Design Lens
Archivist, Voices From the Rwanda Tribunal <http://tribunalvoices.org>
Value Sensitive Design Research Lab <http://vsdesign.org>
University of Washington
There is an old Vulcan saying: "Only Nixon could go to China."
On Nov 12, 2015, at 4:29 PM, Johnny Billquist
<bqt at Update.UU.SE> wrote:
On 2015-11-12 19:49, Al Kossow wrote:
channel
was different.
On 11/12/15 7:27 AM, Jon Elson wrote:
Aha. Interesting. I didn't know that the bit patterns of the control LINCtape is essentially identical to DECtape. I
think the directory
format is different, but I think the block format is the same. I think
the tapes are wound in reverse order and the order of increasing block
numbers is reversed.
Actually the block format is different. "Obverse Compliment" encoding
was created for DECtape. LINCtape blocks aren't bidirectional.
Curious question then - could most DECtape controllers even read
LINCtpae?
I know the TD8E can. The most stupid controller on the planet, but it
enables you
to deal with just about any DECtape format you could possibly
ever invent.
But other DECtape controllers might not be able to deal with tapes that
use other
codes to indicate what is being read...?
I believe you can do this on the TC11 with the READ-ALL operation, but my
memory is vague and the manuals I have handy aren't detailed enough.
paul
6:43 p.m.
On 2015-11-13 00:27, Ian S. King wrote:
PIP10 will let you read (and ISTR, write) PDP-10
formatted tapes on a
PDP-8/TC08. Been there, done that. I don't know if there would be a
problem on a TD8E setup. -- Ian
No, PIP10 knows of both the TC08 and TD8E. If you ever read the PIP10
source code, you'll see the drivers for both controllers in the code.
(Yay for OS/8. Any program wanting to deal with a device in any way
beyond the very basic as to have its own drivers for the device. OS/8
device drivers are super primitive...)
However, that is still dealing with DECtapes. I'm curious about the
ability to deal with LINCtapes, that don't use the same codes on the
mark track (or whatever it was called, my memory fails me at the moment).
The TD8E do not understand things at all, and everything have to be done
in software, which is why I'm saying that it will actually deal with the
LINCtape format if you want it to.
However, more "intelligent" controllers do all this processing of the
mark track to identify start and end of block/tape, and all other
processing, in the controller. Can you make them read out the contents
and do the processing if you have different control codes?
Johnny
On Thu, Nov 12, 2015 at 1:42 PM, Paul Koning <paulkoning at comcast.net> wrote:
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt at softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
On Nov 12, 2015, at 4:29 PM, Johnny Billquist
<bqt at Update.UU.SE> wrote:
On 2015-11-12 19:49, Al Kossow wrote:
channel
was different.
On 11/12/15 7:27 AM, Jon Elson wrote:
> LINCtape is essentially identical to DECtape. I think the directory
> format is different, but I think the block format is the same. I think
> the tapes are wound in reverse order and the order of increasing block
> numbers is reversed.
>
Actually the block format is different. "Obverse Compliment" encoding
was created for DECtape. LINCtape blocks aren't bidirectional.
Aha. Interesting. I didn't know that the bit patterns of the control
Curious question then - could most DECtape controllers even read
LINCtpae?
I know the TD8E can. The most stupid controller on the planet, but it
enables you
to deal with just about any DECtape format you could possibly
ever invent.
But other DECtape controllers might not be able to deal with tapes that
use other
codes to indicate what is being read...?
I believe you can do this on the TC11 with the READ-ALL operation, but my
memory is vague and the manuals I have handy aren't detailed enough.
paul
7:16 p.m.
From: Johnny Billquist
Sent: Thursday, November 12, 2015 3:44 PM
However, that is still dealing with DECtapes. I'm
curious about the
ability to deal with LINCtapes, that don't use the same codes on the mark
track (or whatever it was called, my memory fails me at the moment).
Yes, "mark track".
The TD8E do not understand things at all, and
everything have to be done
in software, which is why I'm saying that it will actually deal with the
LINCtape format if you want it to.
Right. The TD8E only sees "single line passed" (= 3 bits of data + 1 bit
of mark) and "four lines passed" (= 12 bits of data + 1 mark code) and is
completely agnostic about the values.
However, more "intelligent" controllers do
all this processing of the
mark track to identify start and end of block/tape, and all other
processing, in the controller. Can you make them read out the contents
and do the processing if you have different control codes?
The state machine implemented in hardware for all the intelligent DECtape
controllers will not recognize the 4-bit LINCtape codes at all, since the
DECtape codes are 6 bits long. You'll just get a MARK Error.
Rich
9:32 p.m.
On Nov 12, 2015, at 7:16 PM, Rich Alderson <RichA
at LivingComputerMuseum.org> wrote:
...
Doesn't read-all leave mark track recognition to software?
paul
However, more "intelligent" controllers
do all this processing of the
mark track to identify start and end of block/tape, and all other
processing, in the controller. Can you make them read out the contents
and do the processing if you have different control codes?
The state machine implemented in hardware for all the intelligent DECtape
controllers will not recognize the 4-bit LINCtape codes at all, since the
DECtape codes are 6 bits long. You'll just get a MARK Error.
13 Nov
13 Nov
4:49 a.m.
On 2015-11-13 01:16, Rich Alderson wrote:
Yes, except it is of course kludgier than that, since DECtape mark codes
are always 6 bits. The PDP-8 scheme of putting in 12 bit words means
they do not align up with the mark codes easily. So, even more bit
fiddling and packing...
That's also why there are actually 129 12-bit words to a block, even
though only 128 is used.
(128 12-bit words are not evenly divisible by 18.)
Thanks. That is what I sortof was suspecting.
Interesting that the LINCtape use 4-bit codes. That makes it even more
incompatible with DECtape.
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt at softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
From: Johnny Billquist
Sent: Thursday, November 12, 2015 3:44 PM
Thanks. I must be getting old. :-)
However, that is still dealing with DECtapes.
I'm curious about the
ability to deal with LINCtapes, that don't use the same codes on the mark
track (or whatever it was called, my memory fails me at the moment).
Yes, "mark track". The TD8E do
not understand things at all, and everything have to be done
in software, which is why I'm saying that it will actually deal with the
LINCtape format if you want it to.
Right. The TD8E only sees "single line passed" (= 3 bits of data + 1 bit
of mark) and "four lines passed" (= 12 bits of data + 1 mark code) and is
completely agnostic about the values. However, more
"intelligent" controllers do all this processing of the
mark track to identify start and end of block/tape, and all other
processing, in the controller. Can you make them read out the contents
and do the processing if you have different control codes?
The state machine implemented in hardware for all the intelligent DECtape
controllers will not recognize the 4-bit LINCtape codes at all, since the
DECtape codes are 6 bits long. You'll just get a MARK Error.
12 Nov
12 Nov
6:59 p.m.
From: Ian S. King
Sent: Thursday, November 12, 2015 3:27 PM
PIP10 will let you read (and ISTR, write) PDP-10
formatted tapes on a
PDP-8/TC08. Been there, done that. I don't know if there would be a
problem on a TD8E setup. -- Ian
PIP10 explicitly includes code to use the TD8E instead of the TC01/TC08;
it checks to find out what kind of controller is in the machine and sets
up the dispatch tables appropriately. I know this, because when I had
to create a new mode in PDP10 to read in and decode ASCII-encoded 36 bit
binaries[1], my code and the TD8E code got in each other's way.[2]
Rich
[1] Specifically, diagnostics for the KI-10 to be read from DECtape after
being compiled on the Toad-1. The only way to get them to the KI was
to ftp the encoded files to my laptop, use Kermit from the laptop to
the 8/e, and PIP10 to scribble them onto a PDP-10 format DECtape. It
was an experience.
[2] Fields, yeah?
1:56 p.m.
On Thu, Nov 12, 2015 at 8:27 AM, Jon Elson <elson at pico-systems.com> wrote:
LINCtape is essentially identical to DECtape. I think
the directory format
is different, but I think the block format is the same.
No, the block format is different, as the mark track symbols are
different. It's similar, but DECtape made improvements to it to
support full bidirectional read/write capability. (Not all DECtape
systems actually would do reverse write. Some didn't even do reverse
read. But the format supports both.)
Also DECtape does not have a specific directory format. It depends on
what computer line you are using (12-bit, 16-bit, 18-bit, or 36-bit),
and in some cases on which operating system you are running. Some
systems have software to access foreign DECtape logical formats; I
think the widest range of DECtape interchange software provided by DEC
was on TOPS-10.
I think the tapes are wound in reverse order
Yes.
3:26 p.m.
On Nov 12, 2015, at 1:56 PM, Eric Smith <spacewar
at gmail.com> wrote:
...
Also DECtape does not have a specific directory format. It depends on
what computer line you are using (12-bit, 16-bit, 18-bit, or 36-bit),
and in some cases on which operating system you are running. Some
systems have software to access foreign DECtape logical formats; I
think the widest range of DECtape interchange software provided by DEC
was on TOPS-10.
Either that, or RT-11. Its FILEX program supports a bunch of different formats including
TOPS-10 format. (It used an odd way to read 36 bit data on a PDP-11 -- not using the read
all command, but using the read data command and grabbing the upper 2 bits from a CSR as
the words passed by. Tricky, you have to keep up with the DMA engine.)
paul
4:17 p.m.
On 2015-11-12 16:27, Jon Elson wrote:
LINCtape is essentially identical to DECtape. I think
the directory
format is different, but I think the block format is the same. I think
the tapes are wound in reverse order and the order of increasing block
numbers is reversed.
The directory format is OS dependent, and not really anything about the
DECtape vs. LINKtape as such.
But yes, LINKtape runs in the opposite direction to DECtape.
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt at softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
10:39 a.m.
I've got over 200 DEC tapes written before 1973 and there are just a couple
where there is any issue. Those with issues have severe wear of the tape
surface. They were system tapes that were in constant service. Usually
you get a couple of cycles of shoe shine and it manages to read anyway. It
is entirely possible that a rewrite of those sectors would clear the issue
entirely.
They are pretty reliable.
Doug
On Thu, Nov 12, 2015 at 6:24 AM, Tom Moss <tomjmoss at googlemail.com> wrote:
I've had very mixed (about 50/50) success with
9-track, but after reading a
bit about DECtape it looks like they should still be holding up nicely.
Anyone care to share their experiences?
--
Doug Ingraham
PDP-8 SN 1175
10:45 a.m.
Excellent, I guess I'll have to get myself a TU56 at some point.
On 12 November 2015 at 15:39, Doug Ingraham <dpi at dustyoldcomputers.com>
wrote:
I've got over 200 DEC tapes written before 1973
and there are just a couple
where there is any issue. Those with issues have severe wear of the tape
surface. They were system tapes that were in constant service. Usually
you get a couple of cycles of shoe shine and it manages to read anyway. It
is entirely possible that a rewrite of those sectors would clear the issue
entirely.
They are pretty reliable.
Doug
On Thu, Nov 12, 2015 at 6:24 AM, Tom Moss <tomjmoss at googlemail.com> wrote:
I've had very mixed (about 50/50) success
with 9-track, but after
reading a
bit about DECtape it looks like they should still
be holding up nicely.
Anyone care to share their experiences?
--
Doug Ingraham
PDP-8 SN 1175
12:07 p.m.
On 11/12/2015 05:24 AM, Tom Moss wrote:
I've had very mixed (about 50/50) success with
9-track, but after reading a
bit about DECtape it looks like they should still be holding up nicely.
Anyone care to share their experiences?
Long, long time ago I had a DECtape that had been severely 'stretched'
by a problem with a drive. Normally when the drive reverses direction,
it is smooth, and the tape stays firmly laying on the read/write head.
But this drive needed adjustment and when the drive stopped after
reverse motion, the motion on the left reel didn't stop as quickly as
the motion on the right reel. Results: the tape would rise above the
head a bit than 'snap' down when motion had ceased and the tension was
re-affirmed. Once, unfortunately when I was out of the room, the tape
flipped off the head and the reels started madly spinning (trying in
vain to tension the tape that was no longer on the head area. Since the
motors were spinning at different speeds (re the 'braking' problem,) the
right reel was spinning faster and 'winning' causing the tape to get
twisted pretty badly into a 1/8 mylar 'rope'.
After powering down the drive and removing the tapes, I carefully
unwound this mess and restored it to the original reel. Part of the
tape where the most twisting had been done was now 'stretched' and only
about 80% of its original width. You would think this would cause a
problem? Not with DECtape. I was able to copy this wounded tape to
another with no more than a few retries. No data loss.
Alas, I tossed the original. It would have been a good trophy.
-Gary
3170
days inactive
3171
days old
18 comments
10 participants
participants (10)
-
aek＠bitsavers.org -
bqt＠update.uu.se -
dpi＠dustyoldcomputers.com -
elson＠pico-systems.com -
go＠aerodesic.com -
isking＠uw.edu -
paulkoning＠comcast.net -
RichA＠LivingComputerMuseum.org -
spacewar＠gmail.com -
tomjmoss＠googlemail.com