SCSI Bus Problem?

From: Gary Hildebrand <ghldbrd_at_ccp.com>
Date: Tue Feb 12 11:05:33 2002

Tothwolf wrote:
>
> On Mon, 11 Feb 2002, Julius Sridhar wrote:
> > On Mon, 11 Feb 2002, Tothwolf wrote:
> >
> > > 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]
> >
> > Ok. First of all, it's MB/s, rather than Mb/s.
>
> *shrug*
>
> Actually, it would have been better to type the whole thing up with 'MHz'
> and bus width, instead of just MB/s, but I was in a hurry. Oh well, use
> Google.
>
> > Second, MB/s is not a good way to describe the bandwidth of the bus
> > for technical reasons. A fast/wide 20MB/s bus looks *nothing* like an
> > ultra 20MB/s bus. This is so because fast/wide is a 10MHz 16-bit bus
> > and ultra is a 20MHz 8-bit bus.
>
> I didn't imply that a "fast-wide" bus was anything like the "ultra" bus.
>
> > Just because they have the same bandwidth doesn't mean anything. An
> > ultra device will run at 10MB/s on a fast/wide bus and a fast/wide
> > device will run at 10MB/s on an ultra bus. Both busses are *capable*
> > of 20MB/s.
>
> Of course the ultra device would run at 10MB/s, a fast/wide bus runs at
> 10MHz, and the ultra device is only 8 bit instead of 16.
>
> > If you have an ultra device and an ultra/wide device on an ultra/wide
> > bus, the ultra device will run at 20MB/s and the ultra/wide device
> > will run at 40MB/s *simultaneously* **on the same bus**.
>
> I'm not disputing that.
>
> > > (info from memory, might be incomplete, inaccurate, etc, etc)
>
> Uhm, I did put a disclaimer in here...
>
> > > 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.
> >
> > Signalling voltages are irrelevant to this discussion.
>
> Actually, I think not. With the way this thread has been going, I think it
> is quite a good idea to mention the differences between "standard", HVD,
> and LVD signaling.
>
> -Toth

Then AFAIK, you can put an Ultra 160 LBD drive on an UW card, and it
will revert to single ended UW operation. HV differential is a world
unto itself.

Gary Hildebrand
ST. Joseph, MO
Received on Tue Feb 12 2002 - 11:05:33 GMT