Help reading a 9 track tape

Paul Koning paulkoning at
Thu Aug 5 15:12:02 CDT 2021

> On Aug 5, 2021, at 3:57 PM, Len Shustek via cctalk <cctalk at> wrote:
> > On Aug 5, 2021, at 8:39 AM, Jay Jaeger via cctech <cctech at> wrote:
> > I know Paul well (we were contemporaries at U. WI).  He does not do that very often.  He did not indicate any issue with a fire at the building that contains his collection when I last spoke with him.
> >
> > He does not actually read "blocks".  He reads the tape in an *analog* fashion, and then processes the results with software.  That is how he recovered the IBM 1410 system tapes and diagnostics, for example.
> >
> > To be honest, I doubt that this content would be such that he would be likely to volunteer.
> Some years ago, inspired by Paul Pierce's earlier program in Java, I wrote similar software in C to decode the analog waveforms from tapes in a variety of formats: 7-track NRZI, 9-track NRZI, PE, and 6250 BPI GCR, and 6-track NRZI for Whirlwind.

I remember reading that -- nice piece of work indeed.  Around the same time I also saw a project along the same lines in Poland, which recovered an interesting body of software for various early Polish machines.

One of these days we hope to read some 10-track 1/2 inch tapes from an Electrologica X1, a very odd format that could be described as "DECtape with variable length blocks".


More information about the cctalk mailing list