Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!munnari!otc!softway!chris
From: chris@softway.oz (Chris Maltby)
Newsgroups: comp.arch
Subject: Re: DMA on RISC-based systems
Message-ID: <1552@softway.oz>
Date: 29 May 89 01:18:35 GMT
References: <46500067@uxe.cso.uiuc.edu> <1989May26.170247.1165@utzoo.uucp>
Organization: Softway Pty Ltd, Sydney, Australia
Lines: 20

In article <1989May26.170247.1165@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes:
> Having the CPU do the copying is not an obviously *un*reasonable idea.
> Much depends on the details.

> DMA historically was more popular than auxiliary memory because memory was
> expensive.  This is no longer true.

Of course, there are many benefits that can be gained by having controllers
with their own buffers. Disk drivers can stop worrying about rotational
placement if the disk controller is providing whole tracks or cylinders
at a time for no extra bus overhead. LAN drivers can avoid copying stuff
like protocol headers etc into and out of main memory.

Generally, the CPU can be a lot smarter about I/O than any brain-damaged
microprocessor controlled device interface.
-- 
Chris Maltby - Softway Pty Ltd	(chris@softway.sw.oz)

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