Re: Disk ][ Launcher (was: Late night musings...)

[nathan@visi.com (Nathan Mates)]

In article <504ruq$orh@news.bconnex.net>,
Jeff Blakeney <jefbla@bconnex.net> wrote:
>nparker@cie-2.uoregon.edu (Neil Parker) wrote:
>>This would NOT be easy to do.

>>For sofware that loads completely into memory and doesn't access the disk
>>once it's booted, this isn't a problem.  But programs that do disk access
>>after booting could be very difficult to convert to the "Disk ][ Launcher"
>>scheme--somebody would have to disassemble the program's custom RWTS and
>>figure out how to replace it with an emulated RWTS without the main program
>>realizing anything had changed.

>>Depending on the program, this could be anywhere from easy to nearly
>>impossible.

>This is where emulating a piece of hardware, like the Mockingboard,
>could also be used.  Emulate the hardware of the Disk ][ controller
>and any RWTS routine that accesses the hardware can be handled without
>a problem.

   I don't supposed you've ever actually done said act of writing an
emulator for anything, let alone programmed an Apple II at the low
level? Basically, an emulator emulates _everything_, because it has
to.  Some program hits the memory locations that control/access the
disk, the emulator _must_ handle it if it wants to emulate anything.

   On the other hand, the Apple II has no emulators because said
functionality is done _in hardware_. There is NO way of trapping the
memory locations that control/access the disk hardware. Emulators have
the luxury/duty of behaving differently when the hardware is hit.  On
the Apple II, there's no _safe_ way to detect, let alone replace
hardware accesses in software. [Except, as Neil said, f***ing around
with a program's source code to find where it hits the disk]

   The fact that emulators work one way does not mean that the real
computer has a chance of duplicating some functionality in software,
especially when hardware is involved.

Nathan Mates
--
<*> Nathan Mates http://www.visi.com/~nathan/      <*>
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