Re: DMA or not DMA...

[pubpc1@library.ucla.edu]

nathan@visi.com (Nathan Mates) 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.

Hmm, I do have the GS running at 13.75MHz, so it may seem to me that
there really is not much of a difference.  The SCSI card I use is the
Apple II HS SCSI.

I really don't notice much of a difference in GS/OS, but it is more
noticeable in ProDOS 8.

Also, booting involves much sequential access (if you installed
the system on a clean/new partition).


>   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.

Nate, I'm hurt.  :)

No, I really don't mind turning DMA off.  I'd rather gain the extra
memory.


>>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.

As noted by others, CD-ROMs are not as important as hard drives
for the GS because of the rather meager selection of GS specific
titles (about 26).  My point is that if the user wants to use a
CD-ROM sometime in the future, there are other slots to plug in
an SCSI card for a CD-ROM.

Single and double-speed CD-ROMs are so slow that DMA _really_
does not make a difference.


>>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.

I've crashed my GS before and when I reboot, the ramdisk is almost
always there with the data intact (unless I invoke the self-test
first).

8MB is nice if you want to manipulate large graphics and digitize
full length songs at a fairly high sampling rate.  It is also nice
if you want to make use of your sound control panel and have the
computer speak all the alerts to you in a digitized voice.  I admit,
I'm guilty of bloating the computer.  :)

For example, I use the GS to print out full paged scanned documements.
These are usually black and white or grayscale images stored as gifs.
With 8MB, I can deal with four of these images simultaneously,
convert them to SHR, switch to a co-loaded paint program, load up
the SHR files in 320 mode, and print to page in high resolution
(the graphics seem huge on screen in 320 mode, but they come out to
almost exactly a page in size with FAX-like resolution on the
printer.)  With a spooler, you can speed up background printing by
dumping the temp files to the ramdisk.  Sure, I could do the printing
on the PC, but sometimes it is a pain switching computers and with
8MB, it is _possible_ to do this on the GS.:)


>   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.

If you wanted DMA, all you need to do is set up a ramdisk at
3MB (for ROM 3) or 4MB (for ROM 1).  I'd rather use most of the
RAM as memory, though.

-Scott G.