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Date:      Sat, 8 Jun 1996 14:05:30 -0400 (EDT)
From:      Peter Dufault <dufault@hda>
To:        petzi@zit.th-darmstadt.de (Michael Beckmann)
Cc:        scsi@freebsd.org
Subject:   Re: Fast SCSI-2 = 6 MB/sec ?
Message-ID:  <199606081805.OAA22866@hda>
In-Reply-To: <Pine.BSF.3.91.960608162724.401A-100000@zit1.zit.th-darmstadt.de> from "Michael Beckmann" at Jun 8, 96 04:39:17 pm

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> 
> I have just installed a Plextor SCSI CD ROM drive in my machine. I had to 
> find out that it supports only 6 MB/sec. Here is the output from dmesg:
...
> I know that the CD ROM drive can never deliver a throughput of 6 MB/sec, 
> (actually, it should deliver around 680 kByte/sec.) but I wonder 
> if the CD ROM drive decreases the performance of the entire bus, thus 
> limiting the bus throughput to 6 MB/sec. Am I right ? Should I be 
> concerned about this and replace the CD drive ?

No - each device will negotiate its own synchronous rate.  The peak burst
data rate for that CD will be 6MB, and you have to assume it will
will properly disconnect and reconnect to permit effective bus utilization.


-- 
Peter Dufault               Real-Time Machine Control and Simulation
HD Associates, Inc.         Voice: 508 433 6936
dufault@hda.com             Fax:   508 433 5267



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