Message-Id: <200308210626.h7L6Qruu007015@turing-police.cc.vt.edu>
To: jw schultz <jw@pegasys.ws>
Cc: linux-kernel@vger.kernel.org
Subject: Re: 48-bit Drives Incorrectly reporting 255 Heads? 
In-Reply-To: Your message of "Wed, 20 Aug 2003 22:38:24 PDT."
             <20030821053824.GA21451@pegasys.ws> 
From: Valdis.Kletnieks@vt.edu
References: <88A7BC80FA2797498AF6D865CAD3EA43180E95@iceman.altiris.com>
            <20030821053824.GA21451@pegasys.ws>
Mime-Version: 1.0
Content-Type: multipart/signed; boundary="==_Exmh_1439855290P";
	 micalg=pgp-sha1; protocol="application/pgp-signature"
Content-Transfer-Encoding: 7bit
Date: Thu, 21 Aug 2003 02:26:53 -0400
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1810
Lines: 47

--==_Exmh_1439855290P
Content-Type: text/plain; charset=us-ascii

On Wed, 20 Aug 2003 22:38:24 PDT, jw schultz <jw@pegasys.ws>  said:

> A 240 head drive would have to have multiple heads per
> surface or the stack of disks on the spindle would be about
> 5 feet tall.

That's an old Jedi mind trick, dating back at *least* as far as the IBM 3350
disk drive from 1976 (the 23xx drives from the S/360 and the 3330/3340 series
had single heads per surface) .  8 14" platters, 317.5M.  16 physical surfaces,
but it reported 30 heads, because each arm had an "inside" and "outside" head :

====\=====\   (arm)
        =================| (platter)
====/=====/   (arm)

The outside heads were tracks 0-15 and servo-1, the inside heads were 16-29
and servo-2.  It was also available with a second fixed-access arm that had enough
heads to read the first 5 cylinders without seeking at all - so that's another 150
heads.  So that gets us to 180... not *quite* 240, but....

And it wasn't 5 foot tall, by a long shot: http://www.columbia.edu/acis/history/mss.html
The last picture has guys standing around a string of 3350 disk drives (the
actual drive was contained in the white head, the blue bottom part was power
supplies and control logic and the like).


--==_Exmh_1439855290P
Content-Type: application/pgp-signature

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.2.2 (GNU/Linux)
Comment: Exmh version 2.5 07/13/2001

iD8DBQE/RGYtcC3lWbTT17ARAnuOAJ9RWn7usXy8rQJFwOZ7bdkyIU3D6QCgxwju
gESMeQ6gdQsUhiPgQXVLrWk=
=TOa0
-----END PGP SIGNATURE-----

--==_Exmh_1439855290P--
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/