Subject: Re: Apple II Csa2 FAQs Applications
Newsgroups: comp.sys.apple2
From: dempson@actrix.gen.nz (David Empson)
Date: Mon, 15 Mar 1999 00:46:07 +1300
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<briansp@HiWAAY.omit-this.net> wrote:

> supertimer@aol.com (Supertimer) wrote:
> >
> >According to Apple and A+ magazine, ProDOS 16 was a completely
> >separate operating system from GS/OS.  ProDOS 16 was a 16-bit
> >shell on top of the same old ProDOS 8 core.  It was 8-bit at heart.
> >GS/OS was a clean slate and pure 16-bit OS.
> 
> As far as i recall, ProDOS-16 was a 16-bit version of the ProDOS
> kernel (though i don't doubt that it still contained a lot of 8-bit
> code) and included, amongst other things, memory management beyond
> 128k.

As I understand it, ProDOS-16 was basically a wrapper around a modified
version of the ProDOS-8 kernel.  All actual disk I/O took place in bank
0 with the kernel and drivers running in emulation mode.  The wrapper
code implements the native entry points, handles mode switches, and
transfers data between bank 0 buffers and the appropriate location in
other banks.

GS/OS is fully native, only switching to emulation mode as required to
use emulation mode drivers, e.g. firmware on I/O cards.

The main reasons GS/OS is so much faster than P16 (when using native
drivers) is that it avoids double-buffering data, doesn't need to switch
modes for each block access, and can make use of multi-block transfers.

> ProDOS-8 was spawned as an application under ProDOS-16 not much
> differently than is is under the GS/OS kernel.

They are loaded in a similar way, but I wouldn't call P8 an
"application".

The OS loader is responsible for swapping the appropriate kernel into
the bank 0 language card (and other parts of bank 0 and 1) as required.
It was rewritten considerably for GS/OS, due to the architectural
differences between P16 and GS/OS.

> And the GS/OS desktop is Mac-like--not Windows-like.

No argument there!

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand