Re: A86: Free memspace

To: assembly-86@lists.ticalc.org
Subject: Re: A86: Free memspace
From: TGaArdvark@aol.com
Date: Fri, 25 Sep 1998 02:58:03 EDT
Delivered-To: assembly-86-outgoing@towerguard.unix.edu.sollentuna.se
Reply-To: assembly-86@lists.ticalc.org


> I just started Asm a while back, and I thought I had figured out from
> context what memory paging was.  But then I saw some other stuff that
> makes me think I was wrong on some points.
> 
> What is memory paging?  Isn't it a way of making the processor able to
> address more memory than it could otherwise?  Can there be an address on
> one page that is the same as an address on another page?

Yes.  The area of RAM from the address, $8000 to $C000 can be swapped.
There are 8 different "pages" that can go in that area.  You tell it which
page to put there through a port.  The ROM is similiar, but it has 16 pages.
Yes, the same absolute address can point to different information which
is why you MUST make sure the right page is up before jumping.  The
ROM also uses a second addressing scheme that uses AHL (the
registers).  This ensures that there is no confusion reguarding which
page to use.

> And where are some spots in memory that I can use for temporary
> storage?  Are there any places in memory that are normally used for
> nothing that I could use for longer term storage?

All of RAM page 1 except the last ~$100 bytes.