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From: "Rodney W. Grimes" <rgrimes@gndrsh.aac.dev.com>
Message-Id: <199508121012.DAA05664@gndrsh.aac.dev.com>
Subject: Re: Upgrade to my machine
To: smp@teal.csn.org (Steve Passe)
Date: Sat, 12 Aug 1995 03:12:12 -0700 (PDT)
Cc: jayk@rahul.net, hardware@freebsd.org
In-Reply-To: <199508112105.PAA29000@clem.systemsix.com> from "Steve Passe" at Aug 11, 95 03:05:18 pm
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> 
> 
> Hello,
> 
> On Fri, 11 Aug 1995, Jay Kirchhoff wrote:
> 
> >I thing IBM has a drive like that.  It had two 2 gig 3.5 drives mounted 
> >in a full height frame. The ad said the two drive were addressed as one 
> >and the data was stripped across them.
> 
> No, the ad I (think) I saw was for a discrete drive.  Really not sure
> why drive makers haven't done this years ago, there are already
> multiple heads (1 per surface), and they are already
> 'spindle-synced'.  The cost would be duplication of head read/write
> circuits and some additional combiner silicon.

The biggest reason they have not done this is there is 1 analog preamp
that sits on the actuator arm with an analog CMOS mux to switch between
heads.  Adding 3 or 7 amplifiers would be a signficant amount of mass
on the actuator causing problems, and putting it farther away causes
signal problems.

You would also seriously increase the cross talk problems in the head to
drive electronics cable when you started to run 4 or 8 analog 50MHz +
data streams down it.  This is a very low voltage high frequency transmission
line and it is hard enough to make 1 work in a strip line design without
stacking 3 or 7 more next to it causing noise.

These are solveable problems, but they are expensive and complicated
to solve.


-- 
Rod Grimes                                      rgrimes@gndrsh.aac.dev.com
Accurate Automation Company                 Reliable computers for FreeBSD