3 Nov
2025
3 Nov
'25
3:08 p.m.
On Mon, Nov 03, 2025 at 02:04:36PM -0500, Paul Koning wrote:
The LINC version, top picture.
This decoded fine.
https://www.pdp8online.com/ftp/images/GJohns/GCJ-seq1.png
This is going to be tougher to recover.
https://www.pdp8online.com/ftp/images/GJohns/dropout.pdf
On Nov 2,
2025, at 8:25 PM, David Gesswein <djg(a)pdp8online.com> wrote:
Looks like this
https://www.ricomputermuseum.org/collections-gallery/interesting_computer_i…
Which one? There are two pictures which look like mirror images. The one on the left
(part of the ad) would be compatible with the way DECtape reels are normally spooled.
I'm puzzled how you would read a tape without
having the mark track. Or do you mean that the two copies of the data tracks are
available as separate signals but the mark track is a single signal (presumably summing
the two mark tracks)? What about the timing track?
Correct both copies of the redundant tracks are brought out separately except
mark. Correct mark is sum of both tracks.
DEC DECtape drives bring out both timing tracks for skew test. This drive
does the same.
Haven't tried but Manchester encoding doesn't need a clock to decode so in
theory you can decode each track and then align to recover data.
Current
project is LINCtapes. Need to do some code changes to merge in my
DECtape decoder. Bottom links are recent stuff.
https://www.pdp8online.com/images/index.shtml
Interesting. Well, we know DECtape was pretty robust, though it *is* possible to wear it
out, I saw id done repeatedly at my college where DECtape was (in 1973) used as the public
file system for RSTS-11. On the other hand, a former DEC guy told about a DECtape reel
that accidentally was run through the laundry (it was in a pocket) and worked just fine
afterwards. :-)
