Re: SIMMS for IIgs

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

william strutts <wrstrutts1@nospam.home.com> wrote:

> "David Empson" <dempson@actrix.gen.nz> wrote in message
> 1exhoic.13sj7e2c7qe9sN%dempson@actrix.gen.nz">news:1exhoic.13sj7e2c7qe9sN%dempson@actrix.gen.nz...
> 
> > You may be lucky that the 4 MB SIMM worked at all.  Apple IIgs
> > SIMM-based memory expansion cards only support 256 KB and 1 MB SIMMs
> > (some only support 1 MB), since the motherboard does the address
> > decoding for DRAM chips (or SIMMs) on the memory expansion card, and it
> > only supports row sizes of 256 KB or 1 MB.  [See the end of this article
> > for exceptions.]
> 
> Why don't two chip simms work on the IIgs?

That one has me puzzled.  Assuming a 1 MB two-chip SIMM is just using
two 1Mx4 RAM chips, I can't see any obvious reason why it wouldn't work.
It could be an issue related to signal loading, but I would have
expected better behaviour from a two-chip SIMM than an 8-chip one.

There is more likely to be a problem with a composite SIMM which does
something nasty like use a chip to remap the memory layout, as this
could introduce signal loading and timing issues.

Signal loading is also likely to be a problem if you try to install a
double-sided SIMM (512 KB or 2 MB).  The extra memory is no use in these
cases anyway.

> Together that brings my main machine up to 5 meg (ROM 3).  I guess that is
> sufficient for most apps right?

Certainly.  That is what I have in my ROM 3, and I normally have it set
to use an 800K RAM disk.

The only problem I ran into was with one of the fax NDAs, which wanted
rather a lot of memory.