tapes as mass storage (sob)

[donn at hp-dcd.UUCP]

I tried (under duress) using a 7 track as a disc, but it didn't work.
The problem was the well known "crap in the gap" problem.  SOME tape
drives are accurate enough that they don't generate crap in the gap, and
SOME are tolerant enough to skip over the crap, but don't count on it.
DecTapes have a "clock track" that is written "once" and used to clock
the bits onto the tape so that physical block length doesn't vary from
write to write.  The clock on 7 track tape is taken from the OR of the 7
bits so if the capstan slips a bit, so do the bits.  

Did you ever try taking moving one of those tapes from one drive to
another; not really likely to work.  Forget about ever getting a
CDC 6400 (at least early '70s vintage) to read such a tape; they had
a real problem with crap in the gap.

Donn Terry
hplabs!hp-dcd!donn