31 Oct
2025
31 Oct
'25
10:39 a.m.
We may have a half a dozen DECtapes, probably from the PDP-6 era,
perhaps with ITS with content...
Is there anyone, preferably in the MIT vicinity, who might have a
working DECtape drive and be willing to try to read the tapes?
Thanks
/guy fedorkow
31 Oct
31 Oct
1:22 p.m.
If you don't find a closer alternative, I have working DECtape drives on my PDP8e (in
California), as well as software that allows me to upload an entire tape image as a binary
file (via Xmodem protocol).
I'd be available to do this sometime after November 11.
Martin
Typing mangled by iPhone
On Oct 31, 2025, at 10:53 AM, Guy Fedorkow via cctalk
<cctalk(a)classiccmp.org> wrote:
We may have a half a dozen DECtapes, probably from the PDP-6 era, perhaps with ITS with
content...
Is there anyone, preferably in the MIT vicinity, who might have a working DECtape drive
and be willing to try to read the tapes?
Thanks
/guy fedorkow
2:12 p.m.
The Rhode Island Computer Museum should be able to read your DECtapes.
Unfortunately the museum is in the process of moving, and will not be set
up for at least another month.
On Fri, Oct 31, 2025 at 1:53 PM Guy Fedorkow via cctalk <
cctalk(a)classiccmp.org> wrote:
We may have a half a dozen DECtapes, probably from the
PDP-6 era,
perhaps with ITS with content...
Is there anyone, preferably in the MIT vicinity, who might have a
working DECtape drive and be willing to try to read the tapes?
Thanks
/guy fedorkow
--
Michael Thompson
12:52 p.m.
Looks like you have closer options. If they get too many read errors I have a
setup which digitizes analog signals and processes them which may be able
to recover tapes. I'm in MD.
On Fri, Oct 31, 2025 at 01:39:24PM -0400, Guy Fedorkow wrote:
We may have a half a dozen DECtapes, probably from the
PDP-6 era, perhaps
with ITS with content...
Is there anyone, preferably in the MIT vicinity, who might have a working
DECtape drive and be willing to try to read the tapes?
Thanks
/guy fedorkow
------------------------------
5:07 p.m.
Maybe Dave’s setup would work best because the reading software would not need to be
concerned with the format of the tape data.
On Nov 1, 2025, at 4:08 PM, David Gesswein via cctalk
<cctalk(a)classiccmp.org> wrote:
Looks like you have closer options. If they get too many read errors I have a
setup which digitizes analog signals and processes them which may be able
to recover tapes. I'm in MD.
> On Fri, Oct 31, 2025 at 01:39:24PM -0400, Guy Fedorkow wrote:
> We may have a half a dozen DECtapes, probably from the PDP-6 era, perhaps
> with ITS with content...
> Is there anyone, preferably in the MIT vicinity, who might have a working
> DECtape drive and be willing to try to read the tapes?
>
> Thanks
> /guy fedorkow
>
>
>
>
> ------------------------------
6:49 p.m.
New subject: How hard would it be to make new dec tape media?
How hard would it be to make new dec tape media?
60 year tape could use a replacement.
Ben.
2 Nov
2 Nov
7:46 a.m.
New subject: How hard would it be to make new dec tape media?
On 11/1/25 20:49, ben via cctalk wrote:
How hard would it be to make new dec tape media?
60 year tape could use a replacement.
Ben.
DecTape is laminated, ie. it has Mylar on both sides of the
oxide. 50 years ago, we made working replacements from 3/4"
instrumentation tape, but it was NOT laminated. It had a
print-through issue where if left sitting for a few months,
it would start getting errors. I have no idea if there is
anywhere you can buy 3/4" instrumentation tape. Maybe you
can get 3/4" video tape.
Jon
11:25 a.m.
New subject: How hard would it be to make new dec tape media?
On 2025-11-02 8:46 a.m., Jon Elson via cctalk wrote:
On 11/1/25 20:49, ben via cctalk wrote:
I forgot to ask the important question.
"how many reels" of dec tape would be wanted for replacement"?
Ben.
How hard would it be to make new dec tape media?
60 year tape could use a replacement.
Ben.
DecTape is laminated, ie. it has Mylar on both sides of the oxide. 50
years ago, we made working replacements from 3/4" instrumentation tape,
but it was NOT laminated. It had a print-through issue where if left
sitting for a few months, it would start getting errors. I have no idea
if there is anywhere you can buy 3/4" instrumentation tape. Maybe you
can get 3/4" video tape.
Jon 
11:43 a.m.
New subject: How hard would it be to make new dec tape media?
On Nov 2, 2025, at 10:46 AM, Jon Elson via cctalk
<cctalk(a)classiccmp.org> wrote:
On 11/1/25 20:49, ben via cctalk wrote:
Bitsavers has the 3M spec for 480 and 481 sandwich tape, I'm not sure which of these
two is what DEC used. It seems crazy, but it can't hurt to ask 3M if they still make
that stuff.
paul
How hard would it be to make new dec tape media?
60 year tape could use a replacement.
Ben.
DecTape is laminated, ie. it has Mylar on both sides of the oxide. 50 years ago,
we made working replacements from 3/4" instrumentation tape, but it was NOT
laminated. It had a print-through issue where if left sitting for a few months, it would
start getting errors. I have no idea if there is anywhere you can buy 3/4"
instrumentation tape. Maybe you can get 3/4" video tape. 
11:55 a.m.
New subject: How hard would it be to make new dec tape media?
-----Oorspronkelijk bericht-----
Van: Paul Koning via cctalk <cctalk(a)classiccmp.org>
Verzonden: zondag 2 november 2025 20:44
Aan: cctalk(a)classiccmp.org
CC: Paul Koning <paulkoning(a)comcast.net>
Onderwerp: [cctalk] Re: How hard would it be to make new dec tape media?
On Nov 2, 2025, at 10:46 AM, Jon Elson via cctalk
<cctalk(a)classiccmp.org> wrote:
On 11/1/25 20:49, ben via cctalk wrote:
Bitsavers has the 3M spec for 480 and 481 sandwich tape, I'm not sure which of these
two is what DEC used. It seems crazy, but it can't hurt to ask 3M if they still make
that stuff.
paul
Getting the tape is one, but who can record the preformatted blocks on the
"virgin" tape?
Henk, PA8PDP
How hard would it be to make new dec tape media?
60 year tape could use a replacement.
Ben.
DecTape is laminated, ie. it has Mylar on both sides of the oxide. 50 years ago,
we made working replacements from 3/4" instrumentation tape, but it was NOT
laminated. It had a print-through issue where if left sitting for a few months, it would
start getting errors. I have no idea if there is anywhere you can buy 3/4"
instrumentation tape. Maybe you can get 3/4" video tape.
12:34 p.m.
New subject: How hard would it be to make new dec tape media?
On Nov 2, 2025, at 2:55 PM, Henk Gooijen via cctalk
<cctalk(a)classiccmp.org> wrote:
That's easy: any DECtape controller can do that with the help of a simple formatting
utility. I even have the source code lying around.
paul
Bitsavers has the 3M spec for 480 and 481
sandwich tape, I'm not sure which of these two is what DEC used. It seems crazy, but
it can't hurt to ask 3M if they still make that stuff.
paul
Getting the tape is one, but who can record the preformatted blocks on the
"virgin" tape?
Henk, PA8PDP
11:06 a.m.
On Nov 1, 2025, at 8:07 PM, Michael Thompson via
cctalk <cctalk(a)classiccmp.org> wrote:
Maybe Dave’s setup would work best because the reading software would not need to be
concerned with the format of the tape data.
> On Nov 1, 2025, at 4:08 PM, David Gesswein via cctalk <cctalk(a)classiccmp.org>
wrote:
>
> Looks like you have closer options. If they get too many read errors I have a
> setup which digitizes analog signals and processes them which may be able
> to recover tapes. I'm in MD.
Is Dave's setup a DECtape drive, with 10 tracks on 3/4 inch width?
Analog capture would be a great option for old tapes. It's likely there will be tapes
that don't read cleanly with standard controllers, but could be recovered with analog
capture and good DSP.
And yes, it would of course deal with odd formats. Then again, reading PDP-10 tapes on a
PDP-11 is easy; RT-11 has a standard utility that does this, using the controller's
standard "read all" command. I'm not sure how a PDP-8 would cope, given
that the standard PDP-8 blocksize is quite different.
One thing an analog capture system would do that DECtapes would have trouble with is
reading LINCtape, because RALL assumes (I believe) standard DECtape mark track codes and
LINCtape has an entirely different mark track.
paul
5:25 p.m.
On Sun, Nov 02, 2025 at 02:06:00PM -0500, Paul Koning wrote:
Is Dave's setup a DECtape drive, with 10 tracks on 3/4 inch width?
Drive is actually LINCtape with weird tape path so DECtapes need to be
respooled on another drive to LINCtape orientation.
Looks like this
https://www.ricomputermuseum.org/collections-gallery/interesting_computer_i…
All tracks are available from the head separately except mark track which
is why I picked it.
Current project is LINCtapes. Need to do some code changes to merge in my
DECtape decoder. Bottom links are recent stuff.
https://www.pdp8online.com/images/index.shtml
Analog capture would be a great option for old tapes.
It's likely there will be tapes that don't read cleanly with standard controllers,
but could be recovered with analog capture and good DSP.
So far not much DSP. Deskew and handling mark track errors seems to get most
blocks.
And yes, it would of course deal with odd formats.
Then again, reading PDP-10 tapes on a PDP-11 is easy; RT-11 has a standard utility that
does this, using the controller's standard "read all" command. I'm not
sure how a PDP-8 would cope, given that the standard PDP-8 blocksize is quite different.
One thing an analog capture system would do that DECtapes would have trouble with is
reading LINCtape, because RALL assumes (I believe) standard DECtape mark track codes and
LINCtape has an entirely different mark track.
Had been using my PDP-8 TD8E to read DEC & LINC tapes then BeagleBone instead
of TD8E. Some of the LINCtapes I could read with the new setup I couldn't read
with the old.
There was PIP10 to read PDP-10 tapes so I think all PDP-8 controllers could
deal with the different block size. LINCtapes have inverted timing track and
different mark track codes. TD8E could read them some with inverter on timing
track signal and special code.
3 Nov
3 Nov
11:04 a.m.
On Nov 2, 2025, at 8:25 PM, David Gesswein
<djg(a)pdp8online.com> wrote:
On Sun, Nov 02, 2025 at 02:06:00PM -0500, Paul Koning wrote:
Which one? There are two pictures which look like mirror images. The one on the left
(part of the ad) would be compatible with the way DECtape reels are normally spooled.
Is Dave's setup a DECtape drive, with 10 tracks on 3/4 inch width?
Drive is actually LINCtape with weird tape path so DECtapes need to be
respooled on another drive to LINCtape orientation.
Looks like this
https://www.ricomputermuseum.org/collections-gallery/interesting_computer_i…
All tracks are available from the head separately
except mark track which
is why I picked it.
I'm puzzled how you would read a tape without having the mark track. Or do you mean
that the two copies of the data tracks are available as separate signals but the mark
track is a single signal (presumably summing the two mark tracks)? What about the timing
track?
Current project is LINCtapes. Need to do some code
changes to merge in my
DECtape decoder. Bottom links are recent stuff.
https://www.pdp8online.com/images/index.shtml
Interesting. Well, we know DECtape was pretty robust, though it *is* possible to wear it
out, I saw id done repeatedly at my college where DECtape was (in 1973) used as the public
file system for RSTS-11. On the other hand, a former DEC guy told about a DECtape reel
that accidentally was run through the laundry (it was in a pocket) and worked just fine
afterwards. :-)
paul
Analog capture would be a great option for old
tapes. It's likely there will be tapes that don't read cleanly with standard
controllers, but could be recovered with analog capture and good DSP.
So far not much DSP. Deskew and handling mark track errors seems to get most
blocks.
11:46 a.m.
On 2025-11-03 12:04 p.m., Paul Koning via cctalk wrote:
Interesting. Well, we know DECtape was pretty robust,
though it *is* possible to wear it out, I saw id done repeatedly at my college where
DECtape was (in 1973) used as the public file system for RSTS-11. On the other hand, a
former DEC guy told about a DECtape reel that accidentally was run through the laundry (it
was in a pocket) and worked just fine afterwards. :-)
Yes, a tape with clean data.
paul
For trash tapes, could one twist the tape to wind it upside down,do a
bulk erase on it, and reformat it.Ben.
PS: if that fails give it a good wash. :)
12:04 p.m.
On Nov 3, 2025, at 2:46 PM, ben via cctalk
<cctalk(a)classiccmp.org> wrote:
On 2025-11-03 12:04 p.m., Paul Koning via cctalk wrote:
Eek.
Interesting. Well, we know DECtape was pretty
robust, though it *is* possible to wear it out, I saw id done repeatedly at my college
where DECtape was (in 1973) used as the public file system for RSTS-11. On the other
hand, a former DEC guy told about a DECtape reel that accidentally was run through the
laundry (it was in a pocket) and worked just fine afterwards. :-)
Yes, a tape with clean data. paul
For trash tapes, could one twist the tape to wind it upside down,do a bulk erase on it,
and reformat it.Ben.
1:32 p.m.
On 2025-11-03 1:04 p.m., Paul Koning wrote:
Wind it upside down? Not sure what that means. You
could certainly reformat DECtape any time you want, and that would erase it rather well
since the format program writes everything as it does the job. Bulk erase beforehand
would be ok, sure, but I've never seen that done. We had bulk erasers readily
available if we needed them, so it wasn't lack of equipment.
paul
Idea is to flip the tape over, since I expect that facing the head that
side would have the most wear,so you flip the bottom side
that has the least wear up.
2:16 p.m.
On 11/3/25 15:32, ben via cctalk wrote:
On 2025-11-03 1:04 p.m., Paul Koning wrote:
I believe the Mylar film on the data side of the tape is
MUCH thinner than the backing side.
Jon
Wind it upside down? Not sure what that means.
You
could certainly reformat DECtape any time you want, and
that would erase it rather well since the format program
writes everything as it does the job. Bulk erase
beforehand would be ok, sure, but I've never seen that
done. We had bulk erasers readily available if we needed
them, so it wasn't lack of equipment.
paul
Idea is to flip the tape over, since I expect that facing
the head that side would have the most wear,so you flip
the bottom side
that has the least wear up.
5:37 p.m.
On Nov 3, 2025, at 4:32 PM, ben
<bfranchuk(a)jetnet.ab.ca> wrote:
On 2025-11-03 1:04 p.m., Paul Koning wrote:
Yes, but that's unlikely to work. The protective coating is far thinner than the
substrate (0.04 mil vs. 0.92 mil for #481 tape), see
http://www.bitsavers.org/pdf/dec/dectape/3M_DECtape_Spec_Nov66.pdf for the details.
paul
Wind it upside down? Not sure what that means.
You could certainly reformat DECtape any time you want, and that would erase it rather
well since the format program writes everything as it does the job. Bulk erase beforehand
would be ok, sure, but I've never seen that done. We had bulk erasers readily
available if we needed them, so it wasn't lack of equipment.
paul
Idea is to flip the tape over, since I expect that facing the head that side would have
the most wear,so you flip the bottom side
that has the least wear up. 
6:02 p.m.
On 11/3/25 15:32, ben via cctalk wrote:
On 2025-11-03 1:04 p.m., Paul Koning wrote:
Are we talking inside out, upside down or backward?
Inside out would have the FACE of the tape that originally faced the
reel's core now facing out. Rewind like so: o/o
Upside down would have the EDGE of the tape that used to be closest to
the label side now farthest. Just flip the reel without unwinding the tape.
Backward would be winding the tape to a new reel, so that the END of the
tape that was anchored to the core is now the leading end.
And yes, I know it's not "just" any of those actions. Not relevant to
my question.
Doc
Wind it upside down? Not sure what that means.
You could certainly
reformat DECtape any time you want, and that would erase it rather
well since the format program writes everything as it does the job.
Bulk erase beforehand would be ok, sure, but I've never seen that
done. We had bulk erasers readily available if we needed them, so it
wasn't lack of equipment.
paul
Idea is to flip the tape over, since I expect that facing the head that
side would have the most wear,so you flip the bottom side
that has the least wear up.
3:08 p.m.
On Mon, Nov 03, 2025 at 02:04:36PM -0500, Paul Koning wrote:
The LINC version, top picture.
This decoded fine.
https://www.pdp8online.com/ftp/images/GJohns/GCJ-seq1.png
This is going to be tougher to recover.
https://www.pdp8online.com/ftp/images/GJohns/dropout.pdf
On Nov 2,
2025, at 8:25 PM, David Gesswein <djg(a)pdp8online.com> wrote:
Looks like this
https://www.ricomputermuseum.org/collections-gallery/interesting_computer_i…
Which one? There are two pictures which look like mirror images. The one on the left
(part of the ad) would be compatible with the way DECtape reels are normally spooled.
I'm puzzled how you would read a tape without
having the mark track. Or do you mean that the two copies of the data tracks are
available as separate signals but the mark track is a single signal (presumably summing
the two mark tracks)? What about the timing track?
Correct both copies of the redundant tracks are brought out separately except
mark. Correct mark is sum of both tracks.
DEC DECtape drives bring out both timing tracks for skew test. This drive
does the same.
Haven't tried but Manchester encoding doesn't need a clock to decode so in
theory you can decode each track and then align to recover data.
Current
project is LINCtapes. Need to do some code changes to merge in my
DECtape decoder. Bottom links are recent stuff.
https://www.pdp8online.com/images/index.shtml
Interesting. Well, we know DECtape was pretty robust, though it *is* possible to wear it
out, I saw id done repeatedly at my college where DECtape was (in 1973) used as the public
file system for RSTS-11. On the other hand, a former DEC guy told about a DECtape reel
that accidentally was run through the laundry (it was in a pocket) and worked just fine
afterwards. :-)
1:09 p.m.
On Nov 2, 2025, at 8:25 PM, David Gesswein
<djg(a)pdp8online.com> wrote:
On Sun, Nov 02, 2025 at 02:06:00PM -0500, Paul Koning wrote:
Nice. I looked at one of them and saw a picture of the tape:
https://www.pdp8online.com/ftp/images/system_source/LINC/AJH-LAP6-A-t1.jpg
That's interesting because it shows the tape part number "489", not 480 or
481 which is what is shown in the spec captured on Bitsavers.
Doubly interesting because 489 is the specified tape media type (in 1/2 inch width,
though) for the Electrologica X1 tape drives, which are somewhat DECtape like in that they
support random writing.
paul
Is Dave's setup a DECtape drive, with 10 tracks on 3/4 inch width?
Drive is actually LINCtape with weird tape path so DECtapes need to be
respooled on another drive to LINCtape orientation.
Looks like this
https://www.ricomputermuseum.org/collections-gallery/interesting_computer_i…
All tracks are available from the head separately except mark track which
is why I picked it.
Current project is LINCtapes. Need to do some code changes to merge in my
DECtape decoder. Bottom links are recent stuff.
https://www.pdp8online.com/images/index.shtml
11
days inactive
15
days old
22 comments
10 participants
participants (10)
-
ben -
David Gesswein -
Doc Shipley -
Guy Fedorkow -
Henk Gooijen -
Jon Elson -
Lars Brinkhoff -
Martin Eberhard -
Michael Thompson -
Paul Koning