Re: [OpenBIOS] Why protected mode?

[Timothy J. Massey]

On Thu, 15 Jul 1999 15:03:45 -0400 (EDT), Kevin P Lawton wrote:
> Should have dropped real mode, had the CPU start
> out in protected mode, and today we'd all have
> protected mode only BIOSs.  Oh well, such is life.

And how would these computer have run DOS?  Or Windows?  The only OS
available before 1994 or so that didn't use real mode code was OS/2.  Did
everybody switch over to OS/2?  So how could Intel drop real mode?  In fact,
people's biggest complaint with OS/2 in the late 80's was OS/2 Compatibility
Box:  the way that it ran real-mode DOS programs.  If people weren't willing
to use an OS that allowed them to run a decent percentage of their old
software, why would they use a computer that allowed them to run *none* of
their old software!

Think about the difficulty that IBM caused for itself when they dropped ISA
in favor of MicroChannel.  The decision to go MicroChannel was made for
almost identical reasons that you would have wanted Intel to change designs
with the 286:  a better way of doing things.  I think the marketplace voted
on which way they wanted to go...

One other point to run this into the ground:  look at the success that Intel
has had so far in changing their architecture with IA-64.  We've been
waiting for, what?  3 years now?  And with what result?

In an environment as loose as the PC (as the author of Bochs I'm sure
knows), anything that isn't 100% backward compatible is horribly frowned
upon.  Companies like Apple can change CPU designs with success because they
control every detail of the hardware, OS and software.  In the PC world, we
aren't too open to that level of control.

Tim Massey

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Why protected mode?

> And how would these computer have run DOS?  Or Windows?  The only OS
> available before 1994 or so that didn't use real mode code was OS/2.  Did
> everybody switch over to OS/2?  So how could Intel drop real mode?  In fact,
> people's biggest complaint with OS/2 in the late 80's was OS/2 Compatibility
> Box:  the way that it ran real-mode DOS programs.  If people weren't willing
> to use an OS that allowed them to run a decent percentage of their old
> software, why would they use a computer that allowed them to run *none* of
> their old software!

Inside of a v8086 mode, like I mentioned.  Remember, what I
suggested was they went to only 2 modes.  One solid v8086
mode which ran 8086 code well, and one protected mode which
had it's own (clean) architecture.

It would not have been hard for Intel to produce a shell
protected mode executive which did nothing but service v8086 mode code,
as a reference.  This would have allowed all the 8086 code
to run (including DOS), and seeded innovation of OSs.

In this case Windows would have evolved using a cleaner
architecture (the protected mode stuff) while all the
old DOS code would still have ran fine.  I'm not saying
they would have made a better OS though!
> One other point to run this into the ground:  look at the success that Intel
> has had so far in changing their architecture with IA-64.  We've been
> waiting for, what?  3 years now?  And with what result?

Well, it would have been a much different situation making
a move between 8086 and 286 and doing it right from the
beginning, than ramming all that IA32 stuff into a
new VLIW architecture.   Woof.
> In an environment as loose as the PC (as the author of Bochs I'm sure
> knows), anything that isn't 100% backward compatible is horribly frowned
> upon.  Companies like Apple can change CPU designs with success because they
> control every detail of the hardware, OS and software.  In the PC world, we
> aren't too open to that level of control.

Well, like I said, my plan was to give 100% compatibility for
all the DOS progs.  And provide a path to a new and clean
architecture.

Besides that, I don't see anything 100% backward compatible about
any of the x86 chips.  The chapters on differences from the last
chip are a joke.  Try running misbaved programs.

-Kevin
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