Re: Memory Cards - Which to Get?

[dempson@actrix.gen.nz (David Empson)]

Bruce Maples <themaples@worldnet.att.net> wrote:

> I have a ROM 3 w/ the basic 1.25M memory.  Am wanting to move
> it to at least 4 meg (well, 5.25), and was going to get a card
> from Scantron Quality, since I thought that was the only option.
> Then, in reading this group, I've noticed discussion of some other
> cards, and am now confused.
> 
> I thought a 4 meg card was the highest card a GS could take.

It is the highest capacity RAM card that is guaranteed to be compatible
with all DMA devices (provided the card has been implemented correctly).

In a ROM 00/01 IIgs, the maximum total RAM with full DMA support is 4.25
MB.  In a ROM 3, the maximum is 5.125 MB.

The absolute maximum RAM capacity of the IIgs is 8MB of "Fast" RAM
(motherboard plus card) plus the 128KB of "slow" RAM (motherboard only).

In a ROM 00/01, this means that a maxmium of 7.875 MB of card RAM will
be used.

In a ROM 3, a maximum of 7 MB of card RAM will be used.  This _might_
mean that you don't need to fully populate an 8 MB RAM card (it depends
on how the card is implemented, and it may be difficult to determine
which row can be omitted).


If the card provides more than 4MB of RAM, it will not be compatible
with some DMA devices (notably the Apple High-Speed SCSI card).  The
level of compatibility varies.  Some cards are completely incompatible
with the HS SCSI card if they have more than 4 MB installed.  Others
work, but DMA can only be performed in the first 4 MB (the GS/OS drivers
ensure this) so there is a speed penalty with the extra memory.

The RamFast SCSI card uses special techniques to support DMA up to the
8MB boundary.  It claims to support all cards, but I believe that some
still have problems.


Regarding availability: the two major suppliers of RAM cards are Alltech
Electronics (the Sirius card, which uses 1MB 30-pin SIMMs, and holds 4
or 8 MB) and Sequential Systems (two versions of the RamGS: one holds 4
MB and the other holds 8 MB).

-- 
David Empson
dempson@actrix.gen.nz
Snail Mail: P.O. Box 27-103, Wellington, New Zealand