1/2" tape cleaners?

From: Fred N. van Kempen <waltje_at_pdp11.nl>
Date: Sun Oct 24 16:58:45 2004

On Sun, 24 Oct 2004, der Mouse wrote:

> >> Ah... I have never used that facet of 'mt' before
> > You dont need 'mt' (under any UNIX system) to read non-local tape
> > formats.
>
> "Under any UNIX system"? Have you tried them all?
No, but, over the past 20 years, a good selection of them.

> This depends on the drive hardware and the driver. Some tape drives
> really do have fixed hardware block sizes. Even if setting a variable
Yes, such as the half-inch ones, most DAT (DDS1/2 .. /3?) drives
and, I believe, 8mm drives.

> > where usually, a length of 0 indicates an EOF (end of logical file,
> > aka "first tape mark detected") or EOT (end of tape, aka "second
> > consequtive tape mark detected") situation.
>
> If you are using real half-inch tapes, detecting EOT is hard. I've run
> into tapes with a dozen consecutive tape marks and data after them;
> with some hardware, if you keep reading you'll eventually run off the
> *physical* end of the tape - I've done it, and on the less friendly
> drives it's a mess to re-thread the tape enough to rewind it onto the
> original reel.
True... half-inch (and most other fixed-block) drives didnt
do the tapemark thing.

What I forgot to mention was: teh tape-marking "standard" was mostly
a software-based, voluntary standard, to prevent programs from reading
past EOT. Of course, pretty much nothing prevented people from doing
a <TM><TM> sequence, and then writing more data :)

--f
Received on Sun Oct 24 2004 - 16:58:45 BST