SCSI Bus Problem?

From: Tothwolf <tothwolf_at_concentric.net>
Date: Mon Feb 11 18:23:15 2002

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 - 18:23:15 GMT