Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!convex!mic!letni!rwsys!merch!cpe!adaptex!adaptx1!neese
From: neese@adaptx1.UUCP
Newsgroups: comp.periphs.scsi
Subject: Re: SCSI 2 Command Queing
Message-ID: <283400148@adaptx1>
Date: 18 Jun 91 07:37:42 GMT
References: <31293@hydra.gatech.EDU>
Lines: 23
Nf-ID: #R:hydra.gatech.EDU:31293:adaptx1:283400148:000:1147
Nf-From: adaptx1.UUCP!neese    Jun 17 08:44:00 1991


>In <31293@hydra.gatech.EDU> jt34@prism.gatech.EDU (THOMPSON,JOHN C) writes:
>>SCSI 2 supports tagged command queing which I think means that the host may
>>send multiple command requests to the same device. Do most multitasking OSs
>>allow this? Say for example in an UNIX environment that task 1 made a request
>
>I have no idea how to answer for "most" OSs.  For Unix the answer is
>a qualified "of course".  All you need is a driver that knows that
>the hardware can handle it.  The normal disk drivers (block device drivers)
>all have software queueing of requests.  The "elevator" sort is performed
>on the contents of this queue, and one entry is sent out whenever the
>controller is ready.  The driver would have to be restructured to do
>it, but it certainly can be done.  Of course, no such drivers exist in
>the PC Unix world today.

Not quite.  The SCO XENIX 2.3.4 driver and the driver I give out for
a replacement for the standard SCO driver both allow multiple threads
to run on any given target.

			Roy Neese
			Adaptec Senior SCSI Applications Engineer
			UUCP @  neese@adaptex
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