*BSD News Article 3319


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Newsgroups: comp.unix.bsd
Path: sserve!manuel!munnari.oz.au!uunet!usc!sdd.hp.com!elroy.jpl.nasa.gov!ames!sgi!rigden.wpd.sgi.com!rpw3
From: rpw3@rigden.wpd.sgi.com (Rob Warnock)
Subject: Re: Lots of Q's about 386bsd 0.1
Message-ID: <oa5onn0@sgi.sgi.com>
Sender: rpw3@rigden.wpd.sgi.com
Organization: Silicon Graphics, Inc.  Mountain View, CA
Date: Sat, 8 Aug 1992 06:20:30 GMT
Lines: 28

colin@marsh.cs.curtin.edu.au (Colin Manning) writes:
+---------------
| 10)	My hard disks are both Maxtor 7040 AT's.  Do they really only only have
| 5 heads as reported by CMOS, or am I not using a side of a platter??
+---------------

I don't know those particular drives, but a lot of the earlier or smaller
drives use the whole bottom surface as a "servo" surface, that is, magic
prerecorded data that the drive uses to find and lock onto the tracks
(instead of the mechanical detents of *really* old winchesters). So for
an "N"-platter disk, one gets "(2*N)-1" usable data surfaces, and hence,
heads. [Your disks probably have 3 platters.]

Drives with a larger number of platters or tracks have difficulty keeping
alignment between the servo surface and the surface being read/written
across temperature and position changes, so they use "embedded servo", where
the signal from the surface being seek'd on is used to position the heads.
"Embedded servo" drives can use both surfaces of each platter for data.


-Rob

-----
Rob Warnock, MS-9U/510		rpw3@sgi.com
Silicon Graphics, Inc.		(415)390-1673
2011 N. Shoreline Blvd.
Mountain View, CA  94043