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From: carl@CITHEX.CALTECH.EDU.UUCP
Newsgroups: mod.computers.vax
Subject: Re: BIO's vs. DIO's
Message-ID: <870129170732.0kb@CitHex.Caltech.Edu>
Date: Thu, 29-Jan-87 20:07:32 EST
Article-I.D.: CitHex.870129170732.0kb
Posted: Thu Jan 29 20:07:32 1987
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I may be mistaken, but my understanding of the distinction is that whenever
data is actually read from or written to a device, you're talking about direct
I/O; when you issue a call to $QIO(W) that transfers data to or from a buffer
(whether or not it entails actual I/O to a device), that's buffered I/O.
Both types involve the overhead of the call to $QIO(W), but only direct
I/O actually has any cost in terms of communication with the device.