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000174_news@bigblue.oit.unc.edu_Fri May 13 02:18:44 1994.msg
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Received: from bigblue.oit.unc.edu by SunSITE.Unc.EDU (5.65c+IDA/FvK-1.07) with SMTP
id AA02000; Thu, 12 May 1994 23:15:10 -0400
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Date: Fri, 13 May 1994 02:18:44 GMT
From: trumpet-support@petros.psychol.utas.edu.au
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References: <2qrdb3$lr@bmerha64.bnr.ca>, <1994May12.155317.3383@megatek.com>, <arnsteinCppEAr.L72@netcom.com>
Subject: Re: 32 bit access with SCSI no available. Hunh? was Re: Win Mosaic alpha 4 (my fix)
In article <arnsteinCppEAr.L72@netcom.com> arnstein@netcom.com (David Arnstein) writes:
>From: arnstein@netcom.com (David Arnstein)
>Subject: Re: 32 bit access with SCSI no available. Hunh? was Re: Win Mosaic
>alpha 4 (my fix)
>Date: Thu, 12 May 1994 19:04:03 GMT
>In article <1994May12.155317.3383@megatek.com>,
>Antti Tirronen <ajt@megatek.com> wrote:
>>When I had both IDE and SCSI disks installed, I had windows on the IDE disk
>>and it was happy (and faster) with its 32-bit mode. I haven't yet taken the
>>time to try to figure out how to get that back, now that I got rid of the IDE
>>in favor of an all out SCSI system.
>You've discovered the annoying fact that under Windows 3.1 and WFWG 3.11, SCSI
>disk I/O is SLOW, SLOW, SLOW. This is because Windows 3.1 won't do 32-bit disk
>access for (almost all) SCSI host adapters.
>As a result, each time SCSI I/O occurs, Windows must switch from 32-bit
>protected mode to real mode, and run code out of your SCSI host adapters ROM
>BIOS. Doubly slow!
>If you had 32-bit disk access going, Windows would run the code (32-bit disk
>access driver) in protected mode, without touching your SCSI BIOS.
>Only Future Domain host adapters are supplied with a driver that permits 32-bit
>disk access from Windows. This driver does not work with WFWG 3.11 and
>besides, if you do use this driver, you may have to disable 32-bit disk access
>for your IDE drive(s).
>Windows 3.1 users:
> *** J U S T S A Y N O T O S C S I ***
>--
>David Arnstein | What do you mean, "get a life"?
>arnstein@netcom.com | This *is* my life!
On the same subject....
My understanding is that people go for SCSI drives mainly for
following reasons..
- You want oodles of disk space... e.g. 1 Gbyte drives on SCSI are common.
- You're going to need lot's of drives. (More than 2 over IDE can be pain)
- DMA transfers can leave more processor time available for other things in a
server environment.
- you have many more choices on drives since SCSI is popular on other
architectures.
- you can add other peripherals to the SCSI bus. (e.g. tape
backups, scanners)
The down sides are...
- some DMA controllers (e.g. Adaptec) limit the DMA address range to 16M over
an ISA bus. Since it's not uncommon to have more than 16M ram in a
workstation these days, this is a real downer. To work around this, the
drivers have to copy down to < 16M addresses. (This is one of the problems on
petros at the moment since FreeBSD can't do this quite yet)
- You need additional drivers to support them.. (hence the current
discussion) Drivers for popular controller brands are difficult to write
because the companies don't want to give out details of the
controller...(Adaptec for example)
I can live with not having DMA transfers, but the disk size limitations can be
a problem.
My questions are...
Can you buy comparable large hard disks for IDE controllers?
At the same price?
Are the driver problems we are experiencing ever going to be resolved?
Peter