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From: phil@brahms.amd.com (Phil Ngai)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: Questions concerning the Always IN-2000 SCSI controller
Message-ID: <1991Jun12.161207.20292@amd.com>
Date: 12 Jun 91 16:12:07 GMT
References: <50364@ut-emx.uucp>
Sender: usenet@amd.com (NNTP Posting)
Organization: Advanced Micro Devices, Inc.
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bplim@ccwf.cc.utexas.edu (gerald lim) writes:
>However, 
>I've also gotten mail telling me not to get it because it uses PIO.  First,
>does PIO mean Programmed IO?  Second, why is it disadvantageous for a HD/FD
>controller to use PIO?

Yes, PIO is programmed IO. There are several ways of moving data:

1) DMA, which uses the 8237 DMA controllers on the motherboard. Used
for floppies and (I think) the hard disk on the XT. Very slow because
the 8237s are.

2) PIO, the processor moves every byte "by hand". On the 286, this
is quite fast if you use the dedicated string IO instructions. Used
for the disk controller on the AT. (the uP has to read the device
and write memory, so every word takes two transfers)

3) First party DMA or bus master. The peripheral itself takes over
the bus and moves the data directly. Half the transfers of #2
but possible issues with mapping virtual to physical addresses.

--
He cleaned the victims' apartment and then killed them.