Re: Which GS memory card?

[sbehrens@arrowweb.com (S�nke Behrens)]

spec@vax2.concordia.ca (Mitchell Spector) wrote:

>    The Sequential RAM GS Plus (formely made by CV-Technologies and
>known as the CV-RAM) draws very little power and is quite compact in
>size. So much so, it is approximately the size of a 3.5" floppy disk.
>It comes with 4MB soldered in and has sockets to double that to 8MB.
>There was a claim it was DMA compatibly up to 8MB, _if_ you you owned
>a RamFAST SCSI, but I'd question if that's true. At least two owners

Well, I got it equipped with 8MB, have a RF in the system (only device
that does DMA), and a ZIP (the TWGS doesn't support RDY correctly).
Works fine, no problems so far. Certainly no data corruption.

The RF does do some mighty spooky magic to get DMA over all 8MB (it
pulls RDY and basically pretends it's the CPU), and it won't work with
a TWGS (the RF "TWGS" option simply sees to it that DMA above 4MB is
turned off).

>    The Alltech Sirius board in comparison is a larger board (full 
>sized?) and comes with no memory built-in, although Alltech will
>often sell it with some pre-installed. It too expands to a full 8 
>megabytes, although this time using common 1MB SIMM's, such as those
>used in older Macintosh and PC's. Alltech claims it too is DMA 

Which is the reason I'd go with the Sirius. Not only is Alltech
probably the pleasanter company to deal with (Sequential have great
products, but lousy sales and support, in my experience), but 1MB
30-pin SIMMs can be had _dirt_ cheap, whereas 1MBx4 DIPs are almost
impossible to come by (Sequential sells them, at a price).

>    One thing to note, 4MB is the limit for DMA in a ROM 01 (it is 
>5MB in the ROM 3, as it has a full megabyte of 'Fast RAM' soldered 
>to board). In otherwords, both Apple IIgs's can only DMA the first
>4096K it finds in the Memory Expansion slot. To DMA beyond this 
>requires special hardware tricks, as mentioned with the above to 
>memory boards.

True. Keep in mind, though, that there are boards that do "pseudo-DMA"
without special hardware tricks, such as the TurboIDE. The TIDE, in a
nutshell, does this: DMA to the lower 4MB; if the address is above
4MB, DMA to a buffer in low RAM then copy (or it might be switch DMA
off and go directly to upper mem, I have forgotten which one proved
faster).
As a rule, though, boards that were done before the RF and do DMA
(very few, a screen-grabber comes to mind, Apple's SCSI card, and I
think that was it) will fail quite horribly when asked to DMA in a
>4MB expansion RAM system. Particularly nasty with the Apple HS SCSI,
which gets _much_ slower when you turn DMA off.

Yours
Soenke
-- 
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