DMA or not DMA...

[nathan@visi.com (Nathan Mates)]

In article <5kvjei$218i@uni.library.ucla.edu>,
 <pubpc1@library.ucla.edu> wrote:
>I would.  The loss of DMA is not that big of a deal.  In real world,
>random read/write situations, it is not very noticeable (except when
>doing sequential operations like verifying a volume).

   Not that big a deal? I just did some tests on my system (Rev C
RamFAST, fairly minimal set of inits/das, Zip 9/32), and with DMA on,
my GS went from the beep to the GNO/ME boot prompt in ~18 seconds.
Using the RamFAST's control panel to turn off DMA, 23 seconds. That's
adding roughly 30% to a very much real world random access i/o
operation. As the Zip accelerates the non-DMA a good chunk, I'd expect
that the differential would be worse if I turned off my Zip.

   I suspect that you've gone the Siris RAM card (you were claiming
that it had no problems with DMA >4MB a while ago and got promptly
shot down by a whole bunch of people claiming exactly the opposite)
non-DMA route and are making excuses (spelt 'sour grapes') to make
yourself feel good. I do think that a 30% slowdown IS significant, and
I make no excuses or claims to the contrary.

>As for the hard disk, the Focus is good for the new user because
>it really is plug and play.  Upgrading will be harder, though,
>because the drive is mounted on the card (but it is possible).
  
   And this totally contradicts your "get a cd-rom if you can"
advice. You get a focus, you're deadended into a solution you
might be able to swap the drive mechanism, but that's it. SCSI
is far more expandable.

>Thus, 500MB is a safe bet because it gives room to grow.  On the
>otherhand, because the drive does not use DMA, it is a good match
>for future 8MB RAM expansion.

   8MB is also overrated. One memory-trashing bug, and you've most
likely toasted your Ramdisk. [And that happens way too often in a
system without protected memory]. If you want to add lots of
sounds/fonts/inits/das/etc, you invite lots more bugs, and it takes
much longer to read them in, magnified by your 30% non-DMA slowdown.
I've never yet run out of memory on my 4.25MB DMA-happy GS,
despite running lots of big programs at once, 800K swatdisks, etc.

   Once again, you've locked yourself into a slower, non expandable
solution for a GS. Sure, you'll try and compensate for the lack of
drive speed with a Ramdisk, but if you did it right from the start
(spelt: DMA, optional Ramfast), you'd be much better off overall.


   Those of you with HS SCSI cards, I'd invite a few benchmarks of
those with and without DMA (and also with/without any acceleration).
Boot times are a good real-world measurement, as that's something
you'll be sitting through a lot of on the GS.

Nathan Mates
--
<*> Nathan Mates http://www.visi.com/~nathan/      <*>
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