Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!att!mtuxo!mtgzz!drutx!druwy!dlm
From: dlm@druwy.ATT.COM (Dan Moore)
Newsgroups: comp.sys.atari.st
Subject: Re: GDOS vs G+Plus and Revolver & Spectre/PC Ditto
Message-ID: <4109@druwy.ATT.COM>
Date: 12 Jun 89 15:34:40 GMT
References: <8906090028.AA08920@ucbvax.Berkeley.EDU>
Organization: AT&T, Denver, CO
Lines: 35

in article <8906090028.AA08920@ucbvax.Berkeley.EDU>,
01659@AECLCR.BITNET (Greg Csullog) says:
> Finally, Amiga vs ST. The Amiga uses memory paging. Eveything above 512K is
> not main memory but paged memory. Since the Mac needs continuous memory, the
> Amiga version of a Mac emulator cannot run in more than 512K of memory.
> Therefore, unlike Spectre which gives me a 1.7 meg Mac, the Amiga-Mac has
> limited capability (at least that's mu understanding of the situation).

	The Amiga does not use paged memory.  It's just that not all
memory is located at consecutive addresses.  After the first 512K or
1024K of "chip" RAM (Amiga display RAM) there is a large gap before the
next block of RAM.  This is a big difference from the ST and Mac which
assume all memory is in one block starting at address 0.

	AMAX (the Amiga Macintosh emulator) has some advantages and
disadvantages vs. the Spectre.  AMAX can support more memory (> 4 meg)
and can run faster (if you have a 68020 or 68030 in the Amiga). The
Amiga doesn't have ROM in the first 8 bytes of memory so Mac programs
can write there without generating a buss error.  The Amiga hardware
can also read part of a Mac disk directly, no need for custom disk
interface hardware (Spectre GCR or Translator One).  The biggest
disadvantage is lack of hard disk support, unlike the ST there isn't a
standard hard disk interface on the Amiga, all the hard disk
controllers have different interfaces.  (Of course the Magic Sac was
out quite a while before hard disk support was added.)  Also there is
some loss of compatibility when running AMAX and using the
non-contiguous RAM since the Mac assumes all memory is located in one
large block.



				Dan Moore
				AT&T Bell Labs
				Denver
				dlm@druwy.ATT.COM