Path: utzoo!attcan!uunet!samsung!gem.mps.ohio-state.edu!apple!mattd
From: mattd@Apple.COM (Matt Deatherage)
Newsgroups: comp.sys.apple
Subject: Re: II gs Caracteristics
Message-ID: <36028@apple.Apple.COM>
Date: 29 Oct 89 17:35:22 GMT
Organization: Apple Computer Inc, Cupertino, CA
Lines: 58

dcw@athena.mit.edu (David C. Whitney) writes:
>Actually, it only addresses 8mb because it's a port of some sort of
>the mac memory manager. Now, the Mac II is currently "crippled" to
>recognize only 8mb of RAM, even the though the processor can reach
>something like 4gb. As I understand it, the top address lines are not
>used to address memory, but rather as hardware switches. Whenever the
>CPU is asking for very high addresses, the rest of the hardware routes
>that request to the ROM or other hardware (like peripherals - meaning
>the NuBUS).
>
>Even with the virtual memory support of system 7, you won't be getting
>a full 32 bits of address space as RAM. You only get 31 bits. That top
>bit means "select the ROM." Wow, 31 bits of ROM space. They'll never
>fill it up.
>
>At any rate, did ya ever notice that hardware-related addresses in the
>GS are all in high-memory? Perhaps we see a similar design here? Hmm?
>Cost effective? Hmm? Could it be ..... SATAN??? (sorry, couldn't resist :-)
>
>
>Dave Whitney
>dcw@sun-bear.lcs.mit.edu  ...!mit-eddie!sun-bear!dcw  dcw@athena.mit.edu
>My employer pays me well. This, however, does not mean he agrees with me.
>I wrote Z-Link & BinSCII. Send me bug reports. I use a //GS. Send me Tech Info.
Sorry, I don't buy that for one minute.  Most of the IIgs tools were designed
after their Macintosh counterparts, but they were changed everywhere it was
felt appropriate.  For example, the Mac Memory Manager has something similar
to zones, which was not included in the IIgs because it wasn't necessary
Also, the Mac MM doesn't automatically put fixed blocks low and non-fixe
blocks high in memory; the application has to do that with MoveHHi.

The I/O spaces are physically in banks $E0 and $E1, but there are 30 banks
higher than those that don't have I/O spaces.  Also, the I/O can be shadowed
down to banks 0 and 1, so that argument really holds no water either.

Even the new tools are done this way.  The Resource Manager has a similar map
structure to the Macintosh RM, but only at the beginning so the two can tell
each other's files apart.  The Mac Resource Manager gets really slow with large
numbers of resources; the IIgs Resource Manager doesn't.  The Macintos
TextEdit has been revised several times to allow font styling, sizes, colors, 
etc.  It was built into the IIgs one from the beginning (in fact, color was
built into ALL the IIgs tools from the beginning; not so on the Mac!).

No, the reason the Memory Manager only addresses 8 MB is because of hardware
considerations.  But thanks for playing our game anyway; Dave Lyons has 
lovely selection of parting gifts for you.

(I'm horrible.)

-- 
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