Re: IIGS Memory Expansion

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

In article dgc@src.dec.com (Dave Conroy) writes...

>I just picked up a IIGS (ROM01) at a
>thrift store to add to my computer collection, and I'm
>in the process of combining it with other bits and
>pieces I have lying about to make it complete.
> 
>The memory expansion board has 1 bank of 256Kx1 DRAMS on
>it, 3 banks of sockets for additional DRAMS, and two
>jumpers labeled J1 and J2. Could someone who has
>a technical manual handy tell me ...

    That's the 'Apple IIgs Memory Expansion Card', the one sold 
by Apple during the machine's first two years of production (it 
was later included as standard at no extra cost). It comes with
256K soldered-in and expands to a maximum of 1024K (1 MB) total.

>1) will the board accept 1Mx1 DRAMS, or only 256Kx1 DRAMS

    No, it only works with 256Kx1 DRAMs, nothing lower or higher
in density. Make sure you install chips that are at least 150 ns
or faster (i.e. 41256-15) and that they use CAS-before-RAS for
addressing. Not sure how to identify the latter, only which chips
to avoid which don't use it (mail me if you want a list, though
the best way to find out is trial and error by just trying chips :)

>2) the population order for the sockets

    You must populate an entire bank (all eight sockets). For the
lower two banks you must populate _both_ in order for it to work,
so sixteen sockets must be filled. Valid configurations for the
card are 256K (bare card), 512K (upper-bank filled) and 1MB (all
banks filled, including lower). 

>3) the settings for the two jumpers

    Put a jumper on the lower pins (J2) if you populated the top half 
of the board (the sockets next to the soldered-in chips); this is for
512K. If you fill the bottom two banks as well, put a jumper on the
upper pins (J1), which is for a 1 MB configuration.

    So to sum it up and make it clear, either fill just the top eight 
sockets, or fill all the sockets on the card (there are no other valid
ways, so don't try filling just the bottom sockets or half of them).

>I've begun looking in used book stores for bits and
>pieces of IIGS documentation; even though some of the books are
>still in print, my computer collection has a rule that
>it is (generally) forbidden to pay more than the price of
>a computer for it's manuals.

    I generally follow the same rule myself. :) The original manual
for the Apple IIgs wasn't very useful, nor did it contain that much 
technical information. The second revision (for the ROM 3) was a fair 
bit larger and better, but still far from perfect. You should be able 
to find either on comp.sys.apple2.marketplace if you want them.

    In the meantime you might want to read the csa2.FAQ, it's a 
good starting place to find out about the IIgs. I'm working on
an separate Apple IIgs FAQ myself, which will have more in-depth
information and details (it'll be especially useful for people
like yourself who just picked up a GS at a thrift shop or such).
I keep getting side-tracked from finishing it, so I may just
put together a basic FAQ for now and just expand it over the
months (rather than try and finish it all in one shot). I just
don't want to see multiple copies floating around. ;)

Mitchell Spector
spec@vax2.concordia.ca