Pertec Tape Drive Interface Musings
bqt at update.uu.se
Wed Jun 10 14:36:43 CDT 2015
On 2015-06-10 17:05, Dennis Boone wrote:
> > This hypothetical interface + matching software would be intended for
> > archiving old tapes and/or making new copies from archived file
> > (i.e., to make new boot media for bringup of an old computer). Key
> > features would include preservation of block sizes (even if varying
> > arbitrarily) and file marks. I'm not sure if there's already a good
> > file format for that, and I have a dim memory of previously reading a
> > lament about common archival methods failing to preserve blocking.
> The E11/SimH .tap formats are dead simple, and relatively complete as
> far as capturing the arrangement of the bits on tape. They retain block
> size, actual data, file marks, and have a provision for indicating
> errors encountered when reading the tape. There was a discussion
> recently (simh list?) about standardizing the behavior of the error
> marks. The format doesn't have a mechanism for preserving metadata. In
> the SimH variant, record lengths must be even. In the E11 variant, they
> on't have to be. Otherwise, the two are equivalent.
> Using dd to read tapes to disk discards the block size information.
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.
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt at softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
More information about the cctech