Re: Possibility of open-sourcing GS/OS

["Bill Garber" <willy46pa@comcast.net>]

"Ed Eastman" <noone@nowhere.net> wrote in message 
news:dku0be$pq1$1@unlnews.unl.edu...
> Michael J. Mahon wrote:
>> So the bottom line is that, although building a RAM card for the IIgs
>> larger than 4MB is more complex, the 65816 _can_ directly address up
>> to 8MB of RAM.  That could all be used by an operating system, if
>> needed.
>
> The 816 is capable of directly addressing 16M directily through it's 
> internal address registers.  it can be done linearly if you use a latch 
> for the upper 8 bits of the 16 bit address.  The lower 8 bits of the 
> address is the 64k...


If this were true, sounds easy, someone would have done so.
It is not possible to directly access the ram expansion
in the IIgs, regardless of the 65816's capabilities. You
only have a 2 bit row addressing decoder and the address
lines beyond address line 9 are ROM addresses. The first
10 bits is all you have to access ram. The 65816 is much
more powerful that what Apple used. They were very stingy
when they set up the IIgs architecture.

The existing 8 MB cards do not bypass memory manager, they
access it.

Bill Garber