Xref: utzoo comp.arch:6594 alt.next:115
Path: utzoo!hoptoad!pacbell!ames!hc!cs.utexas.edu!milano!bigtex!james
From: james@bigtex.cactus.org (James Van Artsdalen)
Newsgroups: comp.arch,alt.next
Subject: Re: The NeXT Problem
Message-ID: <9287@bigtex.cactus.org>
Date: 15 Oct 88 22:29:34 GMT
References: <26435@ucbvax.BERKELEY.EDU> <7774@gryphon.CTS.COM>
Reply-To: james@bigtex.cactus.org (James Van Artsdalen)
Organization: F.B.N. Software, Austin TX
Lines: 22

In <7774@gryphon.CTS.COM>, richard@gryphon.CTS.COM (Richard Sexton) wrote:

> What makes these drives so slow ? Surely it's not the actuator technology...

It's the mass of the head.  Really fast "conventional" hard disks such
as the CDC Wren-III use a rotary voice coil: the arm turns somewhat
akin to a record player.  The inertia of the head is therefore
critical.  Exiting magentic heads are very lightweight and getting
lighter.  Optics are apparently still very much more massive and could
well remain so indefinitely.  If NeXT has both magnetic and optical
components on the head, it's not clear how they'll ever get the mass
of the head down as low as conventional disks.

As an aside, one interesting idea for linear voice coil drives is to
place several heads along the arm, dramatically cutting the maximum
seek distance.  But it's not clear to me that maximum seek distance is
nearly as important as minimum track-to-track seek time: only stupid
operating systems place data completely at random across a drive (did
someone say AT&T unix? - even MS-DOS does better!).
-- 
James R. Van Artsdalen      james@bigtex.cactus.org      "Live Free or Die"
Home: 512-346-2444 Work: 338-8789       9505 Arboretum Blvd Austin TX 78759