[4164] in linux-scsi channel archive
Re: Ultra Wide (aic-7880) only 20Mbyte/sec?
daemon@ATHENA.MIT.EDU (Georg Koester)
Thu Jun 18 11:52:11 1998
Date: Thu, 18 Jun 1998 17:11:07 +0200
From: Georg Koester <georgk@bigfoot.de>
To: Michael Lausch <mla@gams.co.at>
CC: linux-scsi@vger.rutgers.edu
Hello Michael!
Your adapters maximal transfer rate is indeed 40Mb/sec!
Thats a problem of maths;)
Michael Lausch wrote:
------ snip ------
> (scsi0:0:0:0) Using wide (16 bit) transfers.
> (scsi0:0:0:0) Synchronous at 20.0MHz, offset 8.
> Vendor: IBM Model: DCAS-34330W Rev: S65A
> Type: Direct-Access ANSI SCSI revision: 02
This means, that your bus is running at 20.MHz, but itīs also using wide
negotiation. So you have to double the MHz to get the real
transfer-rate:)
Your calculation would have been right if you had a narrow adapter, thus
one with 8-bit negotiation. With 16-bit your bus transfers two byte with
every Hz.
So the caculation looks like this:
20.000.000 * 2 = 40.000.000 (and thats 40Mb/sec ;)
ciao
> As far as i know, drives with ultra/wide SCSI interface should do 40
> MByte/sec. So why is this disk running at 20Mbyte/sec? The Controller
> BIOS is set up to do 40 MByte/sec on SCSI id 0. The disk shoudl do
> ultra SCSI according to IBM's web pages.
>
> Or ist this message wrong? Just wondering
> --
> Michael Lausch/g.a.m.s. edv dienstleistungen gmbh
> See my web page <http://www.gams.net/~mla> or query PGP key server for PGP key.
> "Reality is that which, when you stop believing in it, doesn't go away".
> -- Philip K. Dick
>
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--
From: Georg Koester e-Mail: georgk@bigfoot.de
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