FW: DecTape & LincTape.

[O. Sharp]

David V. Corbin wrote thus:

> I am tring to remember, what are the differences between DecTape and
> LincTape.....

In addition to tape direction, as someone else already noted, the data 
words are written onto the tape in different bit orders. Here's examples, 
from the LINC-8 and PDP-8 formats:

     LINCtape:              DECtape:
--- timing track  -------  timing track ---
-- 4-bit mark track  ---  6-bit mark track
bit: 0  1  2  3             0  3  6  9
     4  5  6  7             1  4  7  10
     8  9  10 11            2  5  8  11
 [redundant data, mark & timing tracks on other
 side of tape, for both DECtape and LINCtape]

I'm told that DECtape on machines with longer than 12 bits (PDP-9, PDP-10, 
et.al.) continue the data in the same fashion as DECtape, continuing with 
bits 12/13/14 in the next sequential time-track, 15/16/17 in the one
following that, et cetera - though I've never verified it myself.

DECtape also uses 6-bit markers in the mark track, and LINCtape uses 4-bit 
markers; the LINCtape values are given in the PDP-12 Maintenance Manual, 
volume 1, p. 6-11 (and I'm sure the 6-bit DECtape values are somewhere, 
but off the top of my head I don't know where <g!>). I'm also told that 
the timing track for LINCTape is the opposite polarity to that of DECTape. 
This was described to me as a "hidden gotcha".  :)

And that's the sum and scope of my knowledge, thank you very much.

                 -O.-

...Ah, I think I've just found the 6-bit DECtape mark track values. 
They're in the TC08 Maintenance Manual, p. 2-05. Both it and the PDP-12 
maintenance manuals are available on bitsavers.org, which is where I 
first got to see copies. Thanks once more, Al.  :)