>>I'm looking for any information/drivers for qic-02 controllers and the
>>qic-24 format tapes. I've been able to get the driver under Linux
>>(1.2.13) compiled, but without a formated tape to test it, I can't
>>verify if I got everything working or not.
>Does your driver have an "erase" function? That leaves behind a
>valid format, as least on the quarter-inch drives I've dealt with.
Erasing a tape leaves a "valid format" on it? Amazing.
But seriously: I think that the following happened, which left the
impression that the tape was "formatted" by the "erase" function...
When a tape is written in QIC-24 format, it's done in a way that
puts 60MB on a 600 ft tape. When such a tape is subsequently used in
a QIC-150 (or higher) tape drive, the tape drive recognizes that the
tape is written in a lower density than the drive itself is capable
of. As QIC-150 and above drives are *not* capable of writing QIC-24
format tapes (only reading them), it is not possible to overwrite
a QIC-24 format tape in a QIC-150 drive (it will always first "scan"
the tape to see what the existing format is). By erasing the tape,
the tape is effectively wiped of all data (and thus also format);
the same effect can be reached by bulk-degaussing tapes. When you now
attempt to write to the tape, the drive cannot see what the previous
format was, and will write happily.
Note: QIC-525 drives are a bit more intelligent. They also look at the
patterns of holes at the beginning of the tape. These patterns define
the density that the tape is specified for. Thusly it is not possible
to write a QIC-150 tape at QIC-525 density in a QIC-525 drive; the
drive will only allow QIC-150 to be written. It will usually also
completely refuse to write to a QIC-24 tape, because it "knows" (by
looking at the holes) that this is not a format it can write.
Note^2: The above is based on my experiences on a range of tape drives
working from a range of operating systems (although all the tape drives
were SCSI devices). I'm sure there is some drive out there that
contradicts what I have written. All I can be sure of is that the good
old QIC drives do *not* need *any* format of any kind to pre-exist on
the tape; in fact the pre-existance of a format may in fact *prevent*
writing to the tape.
Note^3: QIC means "Quarter Inch Cartridge". Why it's also been used to
describe QIC-40/80 (which I believe to be thinner than 1/4 inch) is a
mystery to me. Is the new "QIC-Wide" now in fact 1/4 inch? :-)
Paul Slootman
--
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Murphy Software, Enschede, The Netherlands
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