Re: //gs Memory 8 or 16megs?

[Roy and/or Janet Miller <millers@inetnebr.com>]

frankc wrote:

> I am under the impression that it does support 8MB of RAM and 8MB of
> ROM.  Not sure how the computer actually seperates the memory or
> if this seperation is even enforced other than in the OS itself.  Can
> anyone fill answer that?  Are apps capable of accessing the full 16MB as
> RAM
> if it were installed or does the OS or BIOS enforce the seperation?  I am
> curious.

Two older computers come to mind that might suggest part of the answer. The
IBM PC's 8088 can address 16 64K sections of RAM, or one megabyte. The same
is true of PC/MS-DOS, however, that memory has to be contiguous, but IBM had
video memory starting somewhere in the 128K just above 640K (depending on the
video card), and that left the upper 1/3 of the memory space for ROM, I/O,
etc. According to Apple's Technical Introduction to the IIGS, memory banks
$E0 and $E1 are system, I/O and display memory, and break the contiguous flow
of Apple IIGS memory, the memory just above those banks are reserved for ROM.

The 68000 in the first four models of the Macintosh could access up to 16
megs of RAM (sound familiar?) however, memory was limited to four megs in the
Plus and SE, even if you used simms larger than one meg. (I believe the Lisa
was also limited to four megs, but getting more than 2 was almost
impossible.) Since the Mac SE, and the IIGS are about the same age, it seems
that in two senses the IIGS was the most advanced machine Apple sold at the
time - it could have twice the memory of the Plus or SE, and it was a full
color display. It wasn't until the Mac II came out that Apple equaled or
exceeded the IIGS in those areas. On the other hand, as Don Lancaster pointed
out in his Ask the Guru column, Apple never even sold a memory card that
would allow the IIGS to have enough memory to run AppleWorks GS comfortably.

Roy