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From: jt34@prism.gatech.EDU (THOMPSON,JOHN C)
Newsgroups: comp.periphs.scsi
Subject: SCSI 2 Command Queing
Message-ID: <31293@hydra.gatech.EDU>
Date: 13 Jun 91 14:47:14 GMT
Distribution: comp.periphs.scsi
Organization: Georgia Institute of Technology
Lines: 18

Excuse me if i posted a similar question but I wasn't sure if I phrased it
correctly so I will try again.
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
to disk 1 and before this request is completed task 2 makes a seperate request
of the same disk 1. Will the OS wait until task 1's request is completed or
with scsi 2 will the OS go ahead and immdeiately send the second request so that
the two requests are being serviced simultaneously. I think scsi 2 allows this
however many OSs and device drivers may not yet support this. Does anyone
know if this is true? Will device drivers need to rewritten for scsi 2 or
can a controller take care of this? A controller can only forward requests it
receives and if the OS won't send more than one at a time you're sunk.
-- 
THOMPSON,JOHN C
Georgia Institute of Technology, Atlanta Georgia, 30332
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