David V. Corbin wrote thus: 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, 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. :)