DECtape reliability?

Johnny Billquist bqt at
Thu Nov 12 17:43:37 CST 2015

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?


> On Thu, Nov 12, 2015 at 1:42 PM, Paul Koning <paulkoning at> wrote:
>>> 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:
>>>> 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
>> 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...?
>> 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

Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol

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