DECtape reliability?

Rich Alderson RichA at
Thu Nov 12 18:16:40 CST 2015

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.


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