Pertec Tape Drive Interface Musings
cclist at sydex.com
Wed Jun 10 11:37:57 CDT 2015
On 06/10/2015 09:12 AM, Mark J. Blair wrote:
> Ok, now three more questions come to mind:
> 1) Is it ever acceptable to mix densities on a single tape? I'm not
> sure that my Kennedy drive will even allow that, but I don't know if
> that is universal.
Acceptable? I don't know about that. Otherwise, it depends on the
drive. Some will allow a density change only at load point.
> 2) What's the scoop on a final record overlapping the EOT marker? Or
> even a new record starting after the EOT marker? I seem to recall
> reading about some applications that stuck data after the EOT, such
> as backup volume information.
Not that unusual--the EOT marker is mostly intended as a warning when
writing. Long-record tapes frequently write past the EOT. On the old
CDC vacuum-column (60x, 65x) drives, I'd sometimes add an extra BOT
marker or two on a reel and start a new "logical tape" there. You just
hit the "LOAD" button again while the tape was already loaded and it
would space down to the next BOT marker. I don't know if anyone else's
drives did that, though. I had my pet deadstart tapes with several
different versions of a system on them.
> 3) Did anybody ever go over to the dark side and implement copy
> protection on magtapes, say, by deliberately including a record with
> bad CRC that a normal driver+drive would not support writing? Or was
> that evil limited to the floppy disk world?
Half-inch tape comes from a more polite, gentler era. Although, on the
7-track drives, you could toggle the parity, which would confuse the
heck out of someone trying to read the tape.
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