Re: ADT Pro With Windows 7 (64-Bit)

[Eric Rucker <bhtooefr@gmail.com>]

On Jun 14, 7:59 pm, Alex Freed <alex_n...@mirrow.com> wrote:
> I didn't look close at the 64 bit AMD/Intel architecture but I wonder
> if it is possible to have an "extender" allowing a particular
> application to use 64 bit registers while running under a 32 bit OS.
> Just like the DOS 32 bit extenders in late 80s.

The thing with the DOS 32-bit extenders is, software running with one
of those didn't have to cooperate with the rest of the system, it just
did everything for itself. And, IA32 allowed running 16-bit or even 8-
bit (reassembled 8080/8085) code while in 32-bit mode.

AMD64/IA32e is a bit different, in that it has two distinct modes for
the CPU. The CPU boots in 32-bit mode, which allows 32-bit, 16-bit,
and 8-bit code. To run 64-bit code, it must switch modes into a 64-bit
mode, at which point it can only run 64-bit and 32-bit code. So, if
you've got any 16-bit apps running, they're gonna fail. Also, I'm not
sure how the rest of the OS would respond to an app throwing it into
64-bit mode, and the implications of an application being able to
switch CPU modes are kinda disturbing, only the kernel should be able
to do that.