General TC11 DECtape diagnostic/formatter questions

Noel Chiappa jnc at
Tue Nov 8 15:43:03 CST 2016

    > From: Josh Dersch

    > If I run them on SIMH configured as an 11/44, I see the same behavior.
    > If I run them on SIMH configured as an 11/20, then I get the printout
    > described in the documentation and listings. ... I haven't yet dug in
    > to see what accounts for the difference -- any ideas?

The fact that the simulator produces identical results to the real hardware
would argue that it's not a bug in that particular hardware. So it must be
some real difference between the two.

There are subtle differences between the 11/20, and other 11's - e.g. on the
/20 SWAB does't clear the V bit - maybe it's one of them? It might be worth
trying setting the CPU type to other values, and see if it works on any other
machine type.

    > 2) I'm looking for means to format DECtapes on the TC11. ... The
    > maintenance manual only indicates "a special program supplied with the
    > TC11 system," and I haven't managed to find it.

The UNIX V6 distro includes a standalone program, tcf.s, to format DECtapes.
I don't know if you have a running V6 system (real or emulated) to assemble
it one; if you want me to assemble it and provide it as binary (in a variety
of formats, e.g. .LDA format), let me know.


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