Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cwjcc!tut.cis.ohio-state.edu!ucsd!hub!dougp
From: dougp@voodoo.ucsb.edu
Newsgroups: comp.sys.amiga
Subject: Re: Seagate \
Message-ID: <2082@hub.UUCP>
Date: 18 Jul 89 03:06:41 GMT
Sender: news@hub.UUCP
Organization: UC, Santa Barbara. Physics Computer Services
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In article <20538@cup.portal.com>, thad@cup.portal.com (Thad P Floryan) writes...
>   as I did at the HD repair place.  But careful examination of the drive
>   clearly shows the "heads" ARE in contact (buffered by the lubrication) with
>   the platter surface during normal operation (determined by sighting across
>   the disk surface looking into a high-intensity lamp).  The head sled is a
>Thad Floryan [ thad@cup.portal.com (OR) ..!sun!portal!cup.portal.com!thad ]

Unfortunatly, "sighting the disk surface looking into a high-intensity
lamp" is not a good enough test in this case to tell if the heads are 
in contact with the disk. Heads fly at an extreemly low altitude (on the
order of the wave length of light), in fact the way the flying hight of
a head is measured is to fly the head on a glass disk, shine white light
through the disk and onto the head, and measure the wavelength of light
which is reflected. (looks like a rainbow since the front of the head
flies higher than the back) This uses the same effect which gives
bubbles their color.

Plated media holds up much better than oxide, where I work, we make
hard disk head testors. We fly heads in a very dusty room to test
and calibrate our testors (we use reject heads and disks). Plated
media seems to last forever, we occaisionaly have to clean the heads,
but the media does not scratch easily. oxide media (especialy 14" disks)
is likely to selfdistruct if it is left flying for several hours.

The purpose of the lubrication is to avoid stiction. dry disks will
stick to the heads and prevent spinning. Too much lubrication will
cause the same problem, depending on the lubricant. Disk manufacturers
like to keep the lubricant they use a secret so I doubt Segate will
tell anyone what they use.

					Douglas Peale