1/4 tape drive formats

[Joseph S. D. Yao]

> Can someone give me a brief description of the differences in the
> formats of 1/4" tape cartridges used on small UNIX systems? In
> particular, do 'archive' and 'streamer' refer to formats on tape, or
> different types of drives, or both? Are these drives or formats
> supposed to be compatible?  ...
> 	Thanks, Bill [johnston at lbl-csam]

"Archive" is the trade name of a certain type of 1/4" tape drive.
It is also the generic name for what we do with 'tar', the Tape
Archiver Program, so I don't know which is correct in your case.

Tar puts out a certain archive format, which you can find in tar(5) of
your 4.2BSD manual.  This is the same format whether you put it on a
raw disc, a raw tape, or into a disc file.  However, it's not much use
if the medium on which you write can't be read by a different device.

A "streamer" is a tape drive which, if fed commands at a high enough
rate, will record or retrieve data on tape at a very high rate of speed.
This is, unfortunately, a very big "if."  Many Unices have just enough
system overhead that they miss the mark.  If the system is just a little
bit slower than the tape drive, the tape drive will: come up to speed to
read/write; find that it's not being given a command before it is done
with that operation; back up to where it should have stopped after the
operation; then, if it sees it now has that command, it will proceed to
operate on it.  Sounds kind of what you describe your Sun as doing.
This means a streamer wins if you can keep it busy, and (probably) loses
if you can't.

According to an Archive advertisement, their drives are streamers.  They
use what they describe as an industry standard, QIC-02 interface and
QIC-24 recording format.  The fact that they feel that they have to say
this implies different recording formats.  There are ANSI standards for
1600 bpi (3200 ftpi), and proposed standards for 6400 bpi and 8000 bpi
(10000 ftpi).  There have been very recently 4-track, 9-track, and
16-track drives. And coding techniques include Phase Encoding (PE),
Group-Coded Recording (GCR), and Inverse Modified Frequency Modulation
(IMFM).

Some of this info must be out of date, as I don't keep close track of
hardware.  And I don't know what kind of 1/4" drives ISI uses -- we
have a 1/2" drive on ours.  But, as you can see, there is a real
possibility that they aren't compatible.  Best solution is to ask your
Sun and ISI reps for technical data on the drives, compare them, and
go back and ask whether the differences you find do make a difference.
You should probably also ask your ISI rep why 'tar u' doesn't work --
I had thought that it should.

(BTW: last thought: if the difference is only one of tape density, but
one of your drives has multi-density capability and a multi-density
controller [do these exist yet for 1/4"?], you may be able to write or
read to a different tape file via 'tar uf /dev/...' and get your files
that way.)

	Joe Yao		hadron!jsdy at seismo.{ARPA,UUCP}