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From: perry@well.UUCP (Perry S. Kivolowitz)
Newsgroups: comp.sys.amiga
Subject: Re: C-Ltd. (Disk Controllers Really)
Message-ID: <2077@well.UUCP>
Date: Thu, 20-Nov-86 23:40:51 EST
Article-I.D.: well.2077
Posted: Thu Nov 20 23:40:51 1986
Date-Received: Fri, 21-Nov-86 05:19:03 EST
References: <2043@well.UUCP> <758@ulowell.UUCP> <1986Nov19.104846.321@utcs.uucp>
Organization: Whole Earth Lectronic Link, Sausalito, CA
Lines: 33
Summary: DMA VS Non-DMA Disk Controllers

In article <1986Nov19.104846.321@utcs.uucp>, wagner@utcs.uucp (Michael Wagner) writes:
> Bob  Page suggested, in his article, that Amiga software would prevent a
> DMA hard disk from performing well.  I don't understand this.  Did I mis-interpret
> his statement?  Or can someone fill me in on this?

The jist of what Bob Page said  (that DMA and Non-DMA disk controllers will
perform at roughly the  same speed)  is correct.  The speed at which a disk
controller can squirt a block to/from the amiga is not the bottleneck.

Witness brand X whose controller  is  capable  of squirts to/from the Amiga
at 300KB/sec (DMA). Compare  this  with  brand  Y whose controller does not
transfer via DMA  and  is  capable of only 100KB peak xfer rate. Which will
run faster? Who knows...it depends on disk layout.

Why? Because the throughput through  the AmigaDOS file system is low enough
that neither controller will  run  at full speed (ie brand X will never get
to really take advantage of the 300KB/sec  since disk i/o time is dominated
by seeeeeeeeeeeeeeeeking).

You may say: But this happens on many systems. You'd be right too. But most
other file system formats do not get  as  scattered  as AmigaDOS can become
after similar interactive useage.

What about super high performance controllers then?

Those wanting to design THE  high performance disk controller for the amiga
will have to look elsewhere for their performance boosts. We (ASDG) are.

Perry

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The above reflects my personal opinion and is the result of my own invest-
igations.