[8697] in linux-scsi channel archive
Re: NCR53C8XX
daemon@ATHENA.MIT.EDU (Drew Eckhardt)
Fri Apr 21 17:27:10 2000
Message-Id: <200004212125.PAA28620@chopper.Poohsticks.ORG>
To: linux-scsi@vger.rutgers.edu
In-reply-to: Your message of "Fri, 21 Apr 2000 16:56:26 EDT."
<20000421205236Z154612-24790+547@vger.rutgers.edu>
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Content-ID: <28614.956352331.1@chopper.Poohsticks.ORG>
Date: Fri, 21 Apr 2000 15:25:38 -0600
From: Drew Eckhardt <drew@Poohsticks.Org>
In message <20000421205236Z154612-24790+547@vger.rutgers.edu>, fheitka@attgloba
l.net writes:
>> > speed of the
>> > lowest device (ie: if you put a 10MB/sec CDROM on an 80MB/sec
>>
>> I was afraid of that too :-(
>
>I don't think that is true. Check out comp.periphs.scsi faq.
It's partially true. If you have a 20M/sec device and 10M/sec device
and the 10M/sec device is capable of a sustained 5M/sec, the 20M/sec
device will only be able to sustain 10M/sec.
Beyond that, your SCSI bus can be set up for single ended signaling, high
voltage differential, or low voltage differential. Mixing and matching is not
possible.
However, most (if not all) LVD devices also support single-ended operation.
If there's a single ended device on the same electical bus, they'll fall
back to single ended operation. While 40MHz clocks are possible with LVD,
you can only run 20MHz on a single ended bus, so having a single ended
device on a bus will limmit you to 20 (8 bit wide) or 40M/sec (16 bit wide).
In many cases, you can work arround this because most single channel
LVD controllers run a bridge chip giving you separate single-ended and LVD
connections on the same logical SCSI bus.
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