Path: utzoo!mnetor!uunet!husc6!m2c!ulowell!page
From: page@swan.ulowell.edu (Bob Page)
Newsgroups: comp.sys.amiga
Subject: Re: 512K expansion for A500
Message-ID: <5692@swan.ulowell.edu>
Date: 24 Mar 88 23:07:05 GMT
References: <919@rmi.UUCP> <26700010@ccvaxa> <5690@swan.ulowell.edu>
Reply-To: page@swan.ulowell.edu (Bob Page)
Organization: University of Lowell, Computer Science Dept.
Lines: 25

Just because it's linked into the system's FAST memory free list
doesn't mean it's fast memory.

>The coprocessors can see this ram when a 1meg Agnus becomes available.

Who said that?  Maybe she can only see in the 0-1MB address range.
Of course, we're talking about a non-item...

The 'ranger memory' at $C00000 is on the same memory bus as CHIP ram
is.  So, the 68K can access it just like CHIP ram.  When you start
using many bitplanes, or go 'blitter nasty', the custom chips steal
memory cycles on THAT particular memory bus.  So even though they
can't SEE that memory, they can still lock out the 68K from seeing it.

On the other hand, 'fast' ram is on a different memory bus, so the 68K
can always have access to it.

Some people call it 'slowfast' ram, some call it 'slow' ram.  It's
linked into the FAST memory list because it isn't CHIP ram.  It's not
CHIP ram because the custom chips can't see it.

..Bob
-- 
Bob Page, U of Lowell CS Dept.  page@swan.ulowell.edu  ulowell!page
		"Nicaragua" is Spanish for "Vietnam."