1 Aug
2026
1 Aug
'26
12:19 p.m.
Dave Gesswein constructed electronics to read the tape data into his laptop
directly from a TU56. We backed up a pdp8, 11, and 10 tape all with the
same process. Dave used a program that I think Vince Briel created, but I
don't know who for sure, to view the tracks individually after import.
This program would show which tracks were all 00's and which were data.
The number of 00 tracks demonstrates whether the tape is 12, 16, 18 bit but
I don't recall exactly how this is done other than to count how many
columns were all 00's. We also viewed wave forms of the data as it was
being inputted.
I also have a TU56 but I have not used it yet. I did some research on the
drive and an interesting negibus/posibus conversion cable that was
apparently used to connect this TU56 to a PDP 9, more info here
https://www.vintagecomputer.net/browse_thread.cfm?id=788
I hopefully will get my TU56 up and running eventually. I donated the
adapter to the RICM a few years ago.
Bill
On Sat, Aug 1, 2026 at 3:49 PM Paul Koning <paulkoning(a)comcast.net> wrote:
On Aug 1, 2026, at 3:00 AM, Bill Degnan via
cctalk <
cctalk(a)classiccmp.org> wrote:
I dont' know. I watched as Dave Gesswein ran them through his TU56.
Did he use read-all mode to read the raw tape structure? Or is this
something lower level still, without using a TC11 controller?
I was
able to load the pdp8 and pdp11 tape
images using simH, I have not
yet tried the pdp10 tape image. The TU56 is a universal drive and as I
underatand it (barely), and if I understand correctly the tracks of 00's
are ignored and/or are used to indicate what kind of system made them,
12,
16, or 18 bit.
True. I remember a DECtape manua, perhaps the TC11/TU56 technical manual,
with an appendix that shows the PDP-n DECtapes for all n, and the matrix of
interoperabiltiy. So if you have a PDP-4 and needed to read PDP-11
DECtapes, it would tell you whether that's possible.
DECtapes basically have a clock track, a "mark" track, and 3 data tracks,
all of these replicated. And controllers like the TC11 have a "read-all"
mode where pretty much everything is extracted, I'm having some trouble
finding out the precise details of how that deals with the block
delimiters, block numbers, etc.
The one thing a TC11 can't handle is LINCtape, because its low level
encoding is different. I think the drive can handle it if you capture the
waveforms, it's compatible at that level, but the controller even in
read-all mode can't cope.
paul