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From: kev@hpcpbla.HP.COM (Kevin Jones)
Newsgroups: comp.periphs.scsi
Subject: Re: 8mm vs. DAT (There ain't no free lunch)
Message-ID: <9850008@hpcpbla.HP.COM>
Date: 14 Nov 90 07:55:58 GMT
References: <65.UUL1.3#1@vortex.COM>
Organization: HP Computer Peripherals Bristol, UK
Lines: 54

There is a degree of truth in the interchange and replayability
"nagging problems". Mechanical aligments of drives (normally from
different vendors) can result in data being recorded at
slightly different azimuths.

AT HP, we did a considerable amount of interchange testing with our
1st generation of DAT products, and found that there was no problem.
We have also done interchange tests between our drives and drives
of other DAT vendors and have not noticed any problems.
DAT drives used for data storage (as opposed to Audio) have a major
advantage in that they can RETRY in the case of an error.
If a slightly misaligned tape is read by a DAT (computer) drive then
you will see some "recovered" errors.
A slightly misaligned DAT (audio) drive CANNOT DO RETRIES (unless
you're prepared to have Beethoven's V'th interrupted repetitively :-),
therefore a failure to recover data on "1st pass" is an unrecoverable
error.

> There have been other problems as well, such as serious tape dropouts

Tape droputs DO EXIST.

> this latter problem may often be related to particular brands of tape

All tapes have "blank spots", where the coating of magnetic particles
on the media is deficient. Some have it more than others.
The good news however is that the majority of these dropouts are
manufacturing defects. Any tape drive with READ-AFTER-WRITE will
detect that it just wrote data over a dropout, and will rewrite that
data until it detects it has placed a perfect copy of that data on
tape. Dropouts for computer tape drives with read-after-write are
therefore a non-problem. (PS. All HP's DAT drives implement
read-after-write).

The audio world is worse off than the computer world when it
comes to dropouts. A sound recording needs a constant data rate.
An audio DAT recorder will not do read-after-write, and even if it
did, then it couldn't take "time off" to rewrite data, since it
would get "out of synch" with the music it was trying to record.


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Kevin Jones.                       | Hewlett Packard Ltd,
                                   | Computer Peripherals Bristol,
kev%hpcpbla@hplb.hpl.hp.com        | Filton Road,
                                   | Stoke Gifford,
Tel: 011 44 272 799910 (ext 22351) | Bristol.   BS12 6QZ.
                                   | ENGLAND.
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