Pertec Tape Drive Interface Musings

[Chuck Guzis]

On 06/10/2015 12:36 PM, Johnny Billquist wrote:

> One problem with "preserving errors" is that actual tapes do not have
> any indication that you have a tape error. In fact, many times you can
> recover a tape block by repeatedly read it. Eventually you might read it
> without errors. Not to mention how many tapes I have "fixed" by just
> folding the tape in the opposite direction where there have been a
> bend/kink in it. Easy fix.
>
> I guess it could possibly be useful to indicate a bad block on a tape,
> in order to preserve the numbering of all the blocks, and constantly
> giving a read error when used in a simulator. But it's kindof a weird
> reflection of a physical error into a virtual one.

...and some errors are correctable by the formatter (and so indicated on 
the interface).  I see no way to indicate that in the SIMH tape proposal.

Earlier, I discussed how I've begun appending metadata to tape image 
files after the EOM indicator.  Thus far, no simulator chokes on it. I 
really need to extend it.  Right now it just indicates date, device 
information, notes from the person doing the reading and error messages 
during reading and file structure; e.g.

536 x 10240 bytes
Filemark at block 537
3 x 80 bytes...

Okay for now; save for a photo of the tape.  Basically, anything known 
before and during reading of the tape and writing of the image.

--Chuck