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Path: utzoo!watmath!clyde!rutgers!brl-adm!brl-sem!ron
From: ron@brl-sem.UUCP
Newsgroups: comp.arch
Subject: Re: Using a DMA chip in strange ways
Message-ID: <630@brl-sem.ARPA>
Date: Tue, 17-Feb-87 22:27:53 EST
Article-I.D.: brl-sem.630
Posted: Tue Feb 17 22:27:53 1987
Date-Received: Thu, 19-Feb-87 06:12:47 EST
References: <4343@columbia.UUCP>
Distribution: world
Organization: Electronic Brain Research Lab
Lines: 19

In article <4343@columbia.UUCP>, dupuy@amsterdam.columbia.edu (Alexander Dupuy) writes:
>     Since the DMA chip on your favorite disk/tape controller works by stealing
> bus cycles when the CPU is busy with other things (like arithmetic), would
> there be any advantage in having a DMA chip which would simply be used for
> memory to memory copies (from user to kernel space, or from one user space to
> another)?
It's a good idea.  I'm glad I've used computers that the designers had
thought of it.  This is used most commonly in certain graphics displays
to make the block memory moves on the display for things like windows
happen faster.

The Denelcor HEP super computer had a block transfer hardware device, but
we never got around to making use of it before we scrapped the thing to
make room for the CRAY.   UNIX could probably see a pretty good speed up
from this thing.  Certain performance studies show that UNIX spends a
majority of it's kernel time shuffling data between the buffer cache and
user data space.

-Ron