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Path: utzoo!watmath!clyde!cuae2!ihnp4!packard!drew
From: drew@packard.UUCP
Newsgroups: comp.sys.ibm.pc,comp.periphs
Subject: Re: Lot's of questions
Message-ID: <550@packard.UUCP>
Date: Mon, 5-Jan-87 01:12:09 EST
Article-I.D.: packard.550
Posted: Mon Jan  5 01:12:09 1987
Date-Received: Mon, 5-Jan-87 06:39:40 EST
References: <9073FIB@PSUVM> <2750@osu-eddie.UUCP> <434@catnip.UUCP> <551@brl-sem.ARPA> <1029@cad.cs.cmu.edu>
Reply-To: drew@packard.UUCP (59452-RD Davis)
Organization: AT&T Bell Laboratories, Liberty Corner
Lines: 46
Keywords: Bernoulli Box
Summary: Why random seeks to preserve Bernoulli media?
Xref: watmath comp.sys.ibm.pc:733 comp.periphs:96

In article <1029@cad.cs.cmu.edu> ralf@cad.cs.cmu.edu.UUCP writes:
>In article <551@brl-sem.ARPA> ron@brl-sem.ARPA (Ron Natalie ) writes:
>>In article <434@catnip.UUCP>, ben@catnip.UUCP (Bennett Broder) writes:
>>> The reason that Bernoulli boxes can't suffer from head crashes is because
>>> the r/w head always contacts the media, just like a floppy disk.
>>Wrong, the bernoulli box is immune from head crashes because it the heads
>>are designed to be able to hit the media, but they are not always in contact
>>with the media.  They achieve their faster turning rates over floppies by
>>forcing air under the heads.
>
>Wrong again:  The Bernoulli Box is so named because it uses the Bernoulli
>effect, in which a rapidly moving stream of fluid (either liquid or gas) 
>experiences a pressure decrease.
>
>The BB can't have a head crash, because in normal operation, the flexible
>media is pulled toward the head by the Bernoulli effect on the air moving
>between the head and the disk surface (this is the opposite of hard disks,
>in which the heads are shaped so that are flowing under them lifts the
>heads off the disk).  If anything interrupts that airflow, such as a piece of
>dirt, the Bernoulli effect is lost, the media is no longer pulled toward the
>heads, and the media is now safely out of harm's way.  THE HEAD NEVER TOUCHES
>THE DISK SURFACE--if it did, the Bernoulli effect would immediately be lost,
>again moving the disk surface away from the head.

I certainly thought that the head never touched the media and that it worked
exactly as described in the preceding paragraph.  But then I got a new
half-height model Bernoulli Box and found it ticked when idle.  The user
documentation explained that this was the sound of random seeks being
automatically performed to prevent wearing out of the media from leaving the
head over just one track.  I wrote to Iomega asking about this and also asked
why they didn't just seek to a dedicated wear-out track instead of making that
constant tick-tick of random seeks.  Their response wasn't too enlightening for
me.  They said that the heads don't really contact the "media" but there is
a lubricant coating the media.  The heads apparently do contact the
lubricant.  (Seemed like word-games to me!)  A dedicated wear-out zone
wouldn't be as good as random seeks because the wear-out zone would run
out of lubricant.  I don't know how to reconcile this statement with my
earlier understanding about the air flow and all that.  Can someone
enlighten me?

I do like Bernoulli Boxes.  I've had some cartridges in use for years and
so far only one cartridge seems to have "worn out" from long use.
(It eventually started to exhibit annoying uncorrectable I/O errors).

R. Drew Davis
ihnp4!packard!drew