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Path: utzoo!watmath!clyde!burl!ulysses!allegra!mit-eddie!think!harvard!seismo!munnari!basser!john
From: john@basser.oz (John Mackin)
Newsgroups: net.unix-wizards
Subject: Re: dump(8) verification ?
Message-ID: <456@basser.oz>
Date: Fri, 11-Oct-85 00:42:58 EDT
Article-I.D.: basser.456
Posted: Fri Oct 11 00:42:58 1985
Date-Received: Mon, 14-Oct-85 03:19:16 EDT
References: <631@dicomed.UUCP> <101@itm.UUCP>
Reply-To: john@basser.oz (John Mackin)
Organization: Dept. of Comp. Science, Univ. of Sydney, Australia
Lines: 30
Summary: not a verify pass

In article <101@itm.UUCP> danny@itm.UUCP (Daniel S. Cox) writes:

>     As a matter of fact, I have access to a Zilog Z8000 machine with a
> cartridge-tape backup.  I don't have source, but during dump(8), in
> level IV, I can hear the tape starting/stoping, then a rewind, then
> some more starting/stopping.  What could this be but a verify?

Ah, the good old Zeus.  But this is no time for reminiscing, you asked
a question.  Here's the answer.

What else could it be?  A lot else.  In fact, what it is, is the tape
changing tracks.  Those cartridge tapes are implemented in the following
way: they have four (or in some cases nine, but the one in the Zeus
is four if I remember right) tracks, but unlike a real magtape the
data is recorded in a bit-serial fashion ON EACH TRACK, not across
the width of the tape (i.e., the read-write head has only one gap,
not four or nine).  The head actually moves up and down relative
to the tape in order to select a track.

Furthermore, the tape can only read/write in the forward direction.
So, to read/write a full tape takes 4 (9) (read/write)-a-track/rewind
cycles.

John Mackin, Basser Department of Computer Science,
	     University of Sydney, Sydney, Australia

seismo!munnari!basser.oz!john	john%basser.oz@SEISMO.CSS.GOV

[By the way, let's have no misunderstandings: my association of
the words "good" and "Zeus" is intended as sarcasm.  Heavy saracsm.]