Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!apple!dlyons
From: dlyons@Apple.COM (David Lyons)
Newsgroups: comp.sys.apple
Subject: Re: Hmm...
Message-ID: <33154@apple.Apple.COM>
Date: 14 Jul 89 20:41:59 GMT
References: <8907121655.AA02954@decwrl.dec.com>
Organization: Apple Computer Inc, Cupertino, CA
Lines: 31

In article <8907121655.AA02954@decwrl.dec.com> secrist@msdsws.enet.dec.com ("Richard C. Secrist") writes:
[...]
>The slots are reserved places in the memory map at $Cn00, where 'n' is
>the slot number.  User space runs through like $BFFF, and backwards from
>that are generally O/S buffers and what not.  Firmware kicks in at $D000
>through $FFFF, and then you're out of memory (so you bank switch).  The
>//gs layered some kind of brain damage on beyond that.

Brain damage??  The Apple IIgs adds another byte to the address bus, so we
have bank numbers.  (This is not bank *switching*--it's actual directly-
addressable memory.)

Bank 0 is the regular 64K; bank 1 is the auxiliary 64K.  Banks $E0 and $E1
are arranged just like 0 and 1 (including I/O space and language card
space), because certain parts of them (screen memory) get shadowed by hardware
(writes to part of 0 and 1 also happen automatically to $E0 and $E1).  $E0/1
are special--they run at 1 MHz for the video circuitry.

Banks 2-$xx (depending on how much memory you have) are plain 64K directly-
addressable memory.

Where's the brain damage?

 --Dave Lyons, Apple Computer, Inc.          |   DAL Systems
   AppleLink--Apple Edition: DAVE.LYONS      |   P.O. Box 875
   AppleLink--Personal Edition: Dave Lyons   |   Cupertino, CA 95015-0875
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   My opinions are my own, not Apple's.