Re: IIgs RAM cards, which one?

[spec@vax2.concordia.ca (Mitchell Spector)]

In article rubywand@swbell.net writes...

>Mitchell Spector writes ...
>>
>>     Well both do tricks in order to bypass the IIgs's 4 MB DMA
>> limit, though neither has been absolutely flawless in doing it
>> from the reports I've heard. Personally, with my own GSes, I've
>> added no more than 4 MB to the expansion slot to avoid the
>> chance of data corruption caused by questionable DMA tricks.
>> I'm not saying don't expand beyond 4 MB, though I would say
>> use caution when doing so.
>
>     Thanks for going into so much detail. Do you know whether or not
>all concerns regarding DMA access have been cleared up regarding 8MB
>IIgs RAM expansions? For example, are there SCSI interface cards which
>must have DMA turned OFF in order to work with either of the 8MB cards
>you mention?

    Well in order to get around the 4 MB DMA limit (note that the
limit is _only_ the expansion slot, motherboard memory is excluded)
you need a RamFAST SCSI card. You also need an 8 MB expansion card
that does DMA properly, and to my knowledge, that only includes the
two currently available cards (I'd be surprised if you could use a
MDIdeas OctoRAM in this situtation).

    I can confirm that the CV-RAM/RAM GS Plus (populated to 5 MB or
more) combined with a RamFAST was _not_ 100% reliable and did often
cause data corruption. The Alltech board was supposed to fix this,
but I thought I heard reports of flakiness with that board as well
in the same configuration. One board is out; but more people need
to share their experiences about the other so we'll know just how
reliable (or not so reliable) it is.

>     Owners of current 8MB cards, including at least one using a current
>RamFAST, have reported difficulties with copying large file blocks
>(>800k) to Zip drive. Do you know anything about this?

    Sounds like problems with DMA, especially if disabling DMA on
the RamFAST SCSI eliminates the problem.

>     Do you know of any popular GS wares which do not function correctly
>with currently available 8MB RAM cards?

    Never heard of anything like that, all (well written) programs and
the GS itself will handle 8 MB of memory just fine (there is no trickery
involved in expanding to 8 MB, anymore than adding 1 MB to the system).
The catch is the lack of DMA availability above the first four megabytes,
and that is when the trickery come into play (doing *DMA* with 5, 6, 7,
or in the case of the ROM 01, 8 megabytes, in the slot). The funny thing
is this wouldn't even be an issue if Apple originally added a simple
third pin to the expansion slot.

>     Regarding the 4MB option, what is your opinion of the board offered
>by MC Price Breakers ...
>
>http://www.mcpb.com/html/ap2ior1.html

    No idea, I've never seen one before (unless it's an OEM version of
a previously made 4 MB card). There were many different memory boards
put out on the market, but not all of them were fully DMA (e.g. Applied
Engineering was notorious for selling flakey RAM boards, despite claims
about full DMA compatibility with the GS). At US$100, I'd say avoid it.

    My opinion in general is stick with 4 MB in the expansion socket,
it is all the memory 99.9% of IIgs programs ever written require (and
it is unlikely at this point you'll see any programs released that
require more). For personal projects it can be handy for creating or
loading in *huge* (at least relative to the IIgs ;) digitized sound
samples, PaintWorks animations or GIF/JPEG images--but beyond that I
don't see the advantage. If you already have an 8 MB card, you can
make things on the safe side if you disable DMA on your hardisk
controller or create a large RAM Disk out of the extra memory.

    Make no mistake -- the GS absolutely needs expanded memory
from what Apple originally included in the box, but you shouldn't go
overboard on the amount _or_ spend more than the whole computer is
worth obtaining that memory (about 3 years back I spent US$25 on
a brand-new RAM GS for my ROM 01 through a close-out sale. I'm
sure similar deals are available on csa2.marketplace if you look
for second-hand cards. Just make sure it is a good card that does
DMA properly, there were about a half dozen or more that were 
quite decent).

Mitchell Spector
spec@vax2.concordia.ca