Ed Eastman wrote:
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...Again, to build a larger ram card means dulpication or bypassing the Memory manager/CYA.
Again, to clarify, I thought that the memory manager was compatible with 8MB of RAM (though DMA is not), and that going into the "ROM" space required changes to the memory manager. Did I get it wrong? I know that the 65816 can _address_ 16MB. Of course, if one is rolling their own OS, then who cares much about Apple's idea of ROM space--unless they cheated in the hardware on the ROM select decoding... -michael Music synthesis for 8-bit Apple II's! Home page: http://members.aol.com/MJMahon/ "The wastebasket is our most important design tool--and it is seriously underused."