FW: DecTape & LincTape.

From: O. Sharp <ohh_at_drizzle.com>
Date: Mon Oct 4 19:27:27 2004

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. :)
Received on Mon Oct 04 2004 - 19:27:27 BST