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DECtape or LINCtape?

NF6X

NF6X

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I recently got three DECtape reels from eBay auctions. One is in a green LINCtape case, and the other two are in blue DECtape cases. I seem to recall reading that DECtape and LINCtape have opposite conventions for which sides the supply and takeup reels go on. All three of my tapes are wound counterclockwise, such that (I think...) the supply reel would mount on the right spindle. Does that imply that all three of my tapes are probably LINCtapes? Can both DECtape and LINCtape reels be read on any PDP-xx system with a TU-5x transport and matching controller?


IMG_8947.jpeg
 
Those are almost certainly LINCtape. The directory listings for the right two appear to be DIAL running on a PDP-12.

I seem to recall it's not exactly possible to read LINCtape on a DECtape system (maybe with a TD8E?), but you can read DECtape on a PDP-12 with a specific option. I guarantee Vince and/or Doug will chime in. :)
 
The PDP-12 System Reference Manual says:

The TC12-F option (prewired) in conjunction with the PRTC12-F program extends the TC12 LINCtape control to read and write DECtapes formatted on the PDP-8, PDP-9, PDP-IQ, and PDP-15 computers.
 
antiquekid3 said:
Those are almost certainly LINCtape. The directory listings for the right two appear to be DIAL running on a PDP-12.

I seem to recall it's not exactly possible to read LINCtape on a DECtape system (maybe with a TD8E?), but you can read DECtape on a PDP-12 with a specific option. I guarantee Vince and/or Doug will chime in. :)
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You are giving me too much credit. I have quite a lot of experience with TU-55 drives and TC01 controller. A lot less experience with LINCtape conventions. I expect that with a lot of work you could read any of those with the TD8E.

The one thing that jumps out at me is that those tapes are all wound like LINC tapes. DECtapes go on the left spindle, over the head and the right side is the take up spool. LINC goes the other way. So as Kyle says, probably all three are LINCtapes.
 
m_thompson said:
...to read and write DECtapes...
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Cool! Have you ever found any information about how the TC-12F is used? It's on my "someday" list to try to understand the code of the program that does accesses, DECtape, but working from the code back to an understanding of what's going on is time consuming.
 
pbirkel@gmail.com said:
I'm guessing that @NF6X objective of (re)using the blue-canister tapes on a non-LINC PDP "ain't gonna happen"?
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Would it be possible to wind the tapes onto a "left-side reel" and then format them for use on a PDP-8? Disclaimer: I've only read some of the documents and have zero practical experience with DECtape.
 
gwiley said:
Would it be possible to wind the tapes onto a "left-side reel" and then format them for use on a PDP-8? Disclaimer: I've only read some of the documents and have zero practical experience with DECtape.
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Yes this will work. There are some LINCtapes which are shorter so won't work but what you have look normal.

Might be good to post pictures of the directory listings to see if anything might be worth reading before overwriting.
 
You might also be able to find someone nearby willing to trade LINCtape for DECtape.

In general I feel that PDP-12 stuff (and LINC-8 stuff) is less available, so it would be better to leave them as LINCtape, I think. Heck, maybe they were once converted the other way and that is why some of the 'tins' are blue.

(There's also a whole crate of NOS DECtape for sale on eBay at the moment.)
 
I've been watching that case of DECtapes on eBay, too. It's tempting, but my excitement is tempered by my limited hope of finding a DECtape drive available for sale at a price I'm willing and able to afford. I'd feel bad about hoarding all of the DECtapes without having a drive to use them with, while there's somebody else out there with a drive and no tapes to use with it.
 
djg said:
Might be good to post pictures of the directory listings to see if anything might be worth reading before overwriting.
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I have neither plans nor ability to overwrite them at this time. In any case, I would archive their contents before considering overwriting them, and I'd happily share any contents that shouldn't be considered personal/private.

Do y'all see anything interesting in these filenames?


IMG_8948.jpeg


Edit:
The green-cased tape did not come with a directory listing, but it has a label:

IMG_8949.jpeg

I purchased all three tapes from eBay seller jcrecycling_2020 in February, 2024.
 
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NF6X said:
I've been watching that case of DECtapes on eBay, too. It's tempting, but my excitement is tempered by my limited hope of finding a DECtape drive available for sale at a price I'm willing and able to afford. I'd feel bad about hoarding all of the DECtapes without having a drive to use them with, while there's somebody else out there with a drive and no tapes to use with it.
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Drives pop up from time to time, often too crusty to make a reasonable restoration project. Mike Thompson has found the heads to be problematic with broken coils and they are potted making the coils difficult to rewind. For Demonstrationss the DECtapes are among the most interesting because they move. Modern computers have no physical moving pieces. Plotters and paper tape readers and punches are next. It is a shame that these peripherals were not saved like the CPU's were.

I've got a couple of hundred reels of the 3M branded tapes where they recorded hailstone strikes on a T-28 while flying through thunderstorms stored on them. (Yes, the pilot seems more than a little crazy to me.) The 3M tapes come in a cardboard box without the fancy round plastic container. I suspect most of them were written and read exactly one time. I still have my original DECtape, the one I paid for with my own money in the College Bookstore sometime in 1975. I have been thinking about what to do with them since the reality is that I only need maybe a dozen. Before I let them go I will have to mount them to make sure they just have the hailstone data, and not an OS/8 style filesystem or DDU images. Hmm, I better explain DDU. DDU stands for DISK DECtape Utility. DDU is a program they wrote to store and restore 64k word DF-32 images on a DECtape. The DF-32 was considered to be volatile and when your machine time was over you had to save your image or your work would be gone. Seems like it took maybe a minute to do a save or restore at most. I think you could store up to 5 DF-32 images on a DECtape. I don't have the source code for it.
 
Oooh! I’ve flown in the back seat of a T-28B several times! Tail number N128KA. Used to belong to an ex boss of mine. No hail was experienced, thankfully.
 
NF6X said:
I have neither plans nor ability to overwrite them at this time. In any case, I would archive their contents before considering overwriting them, and I'd happily share any contents that shouldn't be considered personal/private.

Do y'all see anything interesting in these filenames?


View attachment 1279011


Edit:
The green-cased tape did not come with a directory listing, but it has a label:

View attachment 1279012

I purchased all three tapes from eBay seller jcrecycling_2020 in February, 2024.
Click to expand...
I'd want to image them, in case GAUS, EPINUS, or the Cable Model Programs happened to be the last extant copy of something once sold by DEC, or perhaps another vendor. Finding (or reconstructing) old distributions can be difficult. Imaging isn't too difficult, once one gets to the point one can read and write them. These days the smallest thumb drive will hold a lot of images :).
 
If I could get my hands on even a good DECtape drive head, I think I could make at least a read-only imager. The electronics would be in my area of skill, the mechanical portion of the transport would be more of a challenge for me but still achievable, but the head itself feels inaccessible to me.

On that topic, I would really like to learn how to design multi-track tape heads with geometries suitable for at least DECtape, if not 1/2” 9-track tape. Also how to fabricate prototypes, and how they would typically be mass-produced. How were they made with 1960s technology, and how might we make them with readily accessible technology in 2024?

Do any of y’all have tribal knowledge and/or references to information about practical multi-track tape head design and fabrication? I’ve only ever seen cartoonish sketches of how a tape head works, but never detailed drawings or photographs. Short of sectioning vintage tape heads with sandpaper, I don’t know how I could learn how they’re made.

I currently work at a small defense contractor, and we have a big machine shop with CNC milling machines and lathes, surface grinders, wire EDM, welding, and injection molding. I don’t think I could use any of that equipment off-hours for personal projects, but just for the sake of discussion let’s pretend that we have access to all of those kinds of equipment. My last job was at a company doing veterinary RFID microchips and readers, so let’s also pretend that we have access to coil winders and/or we know how to make them. Feel free to fork this discussion to another topic if desired.
 
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