[OpenBIOS] Why protected mode?

(Kevin P Lawton) bochs at world.std.com
Thu Jul 15 18:47:57 CEST 1999

> 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

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.

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