Re: What is max IIe RAM? 24meg possible? ;-)

[ntt@cleese.apana.org.au (Jonathan Pratt)]

perlockp@cnsvax.uwec.edu writes:
> Just a minor question for those hardware gurus out there who know the normal
> Apple II (not IIgs) system..
> 
> The Applied Engineering memory boards can hold 4 or more megs of RAM 
> (RamFactor III or similar?) and fit on one slot...

Never actually used one myself but most s/w (including ProDOS) only
actually looks for one RAM card, beginning with slot 3, then from 7 to 1. 
You may have to actually write your own software for multiple cards. 
(dunno what comes with RamFactor)

Theoretically, there's no real limit on the amount of memory you have in a
][ system, but you need to be able to address it.  For a non //e (aux
slot) memory card, the info is usualy addressed by bank switching blocks
of 16 K in the same way as the language card use to do. (Titan cards were
like this - they had multiple banks of 16k to give 32k, 64k or 128k of
total expansion RAM)

The //e (aux slot) cards were a little bit easier to use since they
actually switched blocks of 64k which can be addressed using the built in
soft switches.  (you can address various parts of the auxillary RAM with
the soft switches). For cards larger than 64k, you merely have another
location (and there were two that were most popular) which switches
between banks of 64k.  If the location held 00, then the bottom 64 k
(though it doesn't matter) was addressed, an 01 was the next bank, and so
on until the whole card was accessed (1meg = 16  {$00-$0F} banks). 
relatively simple...

If you want to build your own card, get a couple of 16meg SIMMS and attach
them to a card.  All you need now is some memory refresh, address decoding
and bank select (buffer) circuitry.  Stick your card in the aux slot of
the //e and you've got as much RAM as you can afford.  Just gotta write
the software for it.  Not unless you have many other cards, or an aweful
lot of RAM will power consumption or heat dissipation become a major
consideration.

cheers
ntt@cleese