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From: thad@cup.portal.com
Newsgroups: comp.sys.amiga.tech
Subject: Re: 020 and 32 bit memory
Message-ID: <6756@cup.portal.com>
Date: 22 Jun 88 08:25:00 GMT
References: <6339@well.UUCP>
Organization: The Portal System (TM)
Lines: 18
XPortal-User-Id: 1.1001.2826

Yes, there is a good reason why a program will work on an '020 Amiga, then
fail on a system with an '020 and 32-bit-wide memory (look to True Basic
as one example of such failure).  The reason:

some crap software is using the high byte of a 32-bit pointer for some
purpose OTHER than as part of the address (e.g. someone is sticking DATA
into bits 31:24).

On an Amiga withOUT the 32-bit-wide memory, the crap in bits 31:24 is
simply not seen (or, at least, is ignored) by a memory address decoder.

An Amiga WITH 32-bit-wide memory has that memory in the address space ABOVE
the reach of 2^24, and the extra junk WILL be decoded to a non-existent
address.

Rephrased: on a system with 32-bit-wide memory, EVERY bit in an address
pointer is considered to be part of an address; on a "standard" Amiga, only
the information in bits 23:0 are considered part of an address.