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Date:      Mon, 13 Dec 1999 22:33:42 -0700
From:      Brett Glass <brett@lariat.org>
To:        Olaf Hoyer <Inferno@nightfire.de>, chat@FreeBSD.ORG
Subject:   Re: dual 400 -> dual 600 worth it?
Message-ID:  <4.2.0.58.19991213222107.00c7fc20@localhost>
In-Reply-To: <4.1.19991214051944.00c08e80@mail.rz.fh-wilhelmshaven.de>
References:  <Pine.NEB.3.96.991213220754.55242A-100000@shell-2.enteract. com> <4.2.0.58.19991213200556.0473c1e0@localhost>

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At 09:25 PM 12/13/1999 , Olaf Hoyer wrote:

>Hi!
>
>should be shielded cables, or do I miss something about keeping signals clean?

Twisted pairs don't provide the same shielding as coax, but they resist
noise surprisingly well. (It's a standard exercise in advanced E&M physics
classes to show this.) And twists don't lower the impedance as much as a 
shield, nor do they require baluns. If you buy a long differential SCSI
ribbon cable, you'll find that the pairs are twisted within the ribbon. 
(The twists stop at the places where the connectors are crimped
on, then resume.)

>AGP IMHO is some el cheapo implementation of some simple electrical
>prolonging of a simple interface for fast vid transfer, like the VESA local
>bus design in past days.

It is, indeed, a somewhat quick and dirty interface. But it's a good one. 
It does very fast DMA without involving the CPU, which means good
concurrency. In some ways, it's even better suited for hard disks than it
is for graphics!

>Yes, but if someone really needs, say 20 disks/CD-ROMs attached some meters
>away from your box, wouldn't it make sense and be cheaper to put them in a
>dedicated file server /server box and attach them via a fast network?

That's what I'd do. Inside the box, you could use regular IDE for CD-ROMs
or fast interfaces for hard disks. ATAPI is cheap; additional interfaces 
would probably cost about $5 each. Just a few more chips and connectors 
on a PC board. Outside the box, you'd use FireWire, SCSI, fast Ethernet,
or gigabit Ethernet.

--Brett



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