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Path: utzoo!mnetor!seismo!rutgers!topaz!eric
From: eric@topaz.RUTGERS.EDU (Eric Lavitsky)
Newsgroups: comp.sys.amiga
Subject: Re: Hard disk through parallel port
Message-ID: <8088@topaz.RUTGERS.EDU>
Date: Mon, 22-Dec-86 21:33:51 EST
Article-I.D.: topaz.8088
Posted: Mon Dec 22 21:33:51 1986
Date-Received: Tue, 23-Dec-86 00:32:59 EST
References: <634@hp-sdd.HP.COM> <1121@cbmvax.cbmvax.cbm.UUCP> <1527@ulysses.ho <2241@well.UUCP>
Organization: Rutgers Univ., New Brunswick, N.J.
Lines: 76

In article <2241@well.UUCP>, bj@well.UUCP (Jim Becker) writes:
.>In article <1527@ulysses.homer.nj.att.com> eric@ulysses.UUCP (Eric Lavitsky) w
rites:
.>>>George Robbins (cbmvax!grr) Writes:
.>>>Well, since there is no DMA support available for the Parallel Port, the
.>>>actual data transfer part of the disk activity will be slower than a DMA
.>>>type disk controller attached to the Expansion Bus.
.>>
.>>A bit of clarification here: George is correct, but: The only thing DMA
.>>really buys you on the Amiga currently, is the fact that data trasnfers
.>>don't interrupt the CPU. The maximum *actual* throughput for current DMA 
.>>vs. non DMA disks is currently limited by AmigaDOS, which can only chug 
.>>through about 35K/Sec. So, a disk on the parallel port, if designed correctly
.>>will get you at least close to that limit and a DMA disk cannot surpass
.>>that limit (at least not the ones that currently exist). Of course, if
.>>you're not using AmigaDOS, that's another story...
.>>
.>>Eric
>
>Eric,
>
>I know that you are int the know, but in this case you are incorrect. the DMA
>is much faster than what can happen on the parallel port. What transpires on
>the expansion bus if difficult to get used to, although one adapts to the speed
>in time and cna await the 2 to 3x speed improvement in the DOS that is coming.

Well Jim, thank you - I know that you are in the know as well, and I
think that InfoMinder is a great product, but... I never suggested
that there was any DMA on the parallel port, or that the parallel port
was as fast as the expansion bus. I still stand behind what I said.
Perhaps a little further clarification is necessary...

Imagine the following: you drive a Lamborghini :-). Of course, this car
can outpreform just about any other car in America. Bring the car onto
your average American highway however, and you will be forced to do
about the same speed as the other cars on the road (though it may take
you less effort). Why?, because the American roads are so bad they
limit you to a slower speed (this is a documented fact :-)...

So currently (and I underline that word), the bottleneck is AmigaDOS
(as you even pointed out). Yes, it is good news that Tim King has
finally done something about it, and when it's finally generally
available (how long do you think it will take?), there will be no
question that DMA disks are oodles faster than any other. But for now,
everyone has to travel on the same road (note that I'm still talking
about throughput through AmigaDOS, *not* raw data transfer rates).

So: 
	Parallel port 30K/Sec => AmigaDOS =>User ~= 
		Expansion Bus 10Mbit/Sec => AmigaDOS =>User

Does that explain my point better? Another important thing to mention
is that Phil's news about Tim Kings' fixes was news to me after I sent
my message out... so all this may be moot (when the improvements see
the light of customers' hands)...

>The Parallel port doesn't have DMA, but the serial port does. Noone has tapped
>this yet though. It will be inconsiquential though, when the Pal Jr comes out
>there will be a new standard that will take a while for the human to get 
>used to, especially with InfoMinder Plus.

Yes, but to tie up the serial port with a hard disk would be a very
big mistake - one often wants his disk available while online with
another host, you could always wait for the printer, right? :-)

>Amiga will be the future, espiecially if C-A realizes it.
>
>-Jim Becker
>Terrapin Software

Eric (I hate inews) Lavitsky
-- 
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