SCSI Bus Problem?

From: John Chris Wren <jcwren_at_jcwren.com>
Date: Mon Feb 11 19:06:53 2002

        Well, damn, I didn't know that. I thought the controller change speeds to
talk to the device that was being addressed. It makes little sense that the
slowest device should slow down the whole bus to it's speed.

        --John

> -----Original Message-----
> From: owner-classiccmp_at_classiccmp.org
> [mailto:owner-classiccmp_at_classiccmp.org]On Behalf Of Tothwolf
> Sent: Monday, February 11, 2002 19:23 PM
> To: classiccmp_at_classiccmp.org
> Subject: Re: SCSI Bus Problem?
>
>
> On Mon, 11 Feb 2002, Sellam Ismail wrote:
> > On Mon, 11 Feb 2002, Julius Sridhar wrote:
> >
> > > A narrow device will not slow down a wide bus to narrow width. But a
> > > 10 MHz device will slow down a 20 MHz SCSI bus to 10MHz.
> >
> > You're contradicting yourself here. Either that or the semantics of
> > your sentence are confusing :)
>
> SCSI itself is confusing...basically the bus will operate at the fastest
> rate of the slowest device on the bus.
>
> Original - narrow, 5Mb/s [used by lots of older devices]
> Fast - narrow 10Mb/s [very common]
> Ultra - narrow 20Mb/s [very common]
> Wide - wide, 20Mb/s [common for a short time]
> Ultra-Wide - wide, 40Mb/s [very common]
> Ultra2 - wide, 80Mb/s [never really caught on]
> Ultra160 - wide, 160Mb/s [starting to become common]
> Ultra320 - wide, 320Mb/s [not common yet]
>
> (info from memory, might be incomplete, inaccurate, etc, etc)
>
> There are also Differential versions of Fast, Ultra, Wide, and
> Ultra-Wide.
> These use a "high voltage" (+-12VDC IIRC) signaling that is *NOT*
> compatible with standard devices. You will literally fry any non HVD
> devices if you connect a HVD drive to the same bus. Ultra2 and newer have
> a Low Voltage Differential bus, I'm not sure if there is a HVD
> specification for those.
>
> -Toth
>
>
Received on Mon Feb 11 2002 - 19:06:53 GMT