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(a)classiccmp.org
[mailto:owner-classiccmp@classiccmp.org]On Behalf Of Tothwolf
Sent: Monday, February 11, 2002 19:23 PM
To: classiccmp(a)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