[A86] Re: ? [OT]

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[A86] Re: ? [OT]


what?

afaik, 32-bit protected mode has no memory restrictions related to the
8086.
There is a limit to a 4GB address range (per task), but that's because
everything is limited to 32 bits.  Actually, I bet a really sneaky os
could extend that using segment registers, but it wouldn't really be
worth it.

Most of the 8086 instructions are still useful, defaulting to 32 bits
rather than 16.  The main problem with supporting them (besides the extra
hardware to decode them, not a minor issue) is that they take up some of
the shorter (8-bit) opcode values forcing newer instructions to be
longer.  Variable length instructions are generally a bad thing anyway
for modern processors.

Have you seen anything about IA-64?  It has "modes" supporting older
processors as intel has done in the past, but in the native ia64 mode,
older instructions *aren't* supported.  Instructions are packed into
fixed length structures (up to 3 in each 128-bit "bundle"), there's two
large register stacks, predicate registers for conditional execution
(less cmp/jmp speedbumps).  It really seems optimized for c-like
languages.  They don't seem to have left themselves room to add extra
features tho. (like MMX, SIMD, etc)

*sniff* and there's no rotate instruction!!

and to get *really* picky ;), "of equal speed" doesn't mean anything.  I
could say they're "of equal speed" if the take the same amount of time
for a given task.  Then, by definition, that Mac couldn't take less time
if it's of equal speed.  You could say they're of equal speed if a given
instruction takes the same amount of time.  Then it's a matter of which
takes more instructions for the task.  You could say equal clock speed,
then even previous generations of x86 chips would finish in less time.  A
better measurement might be of equal cost or equal heat output.

-josh


On Tue, 6 Mar 2001 23:22:19 -0600 (CST) Shawn Ells <sells@inetnebr.com>
writes:
> 
> In all accuality we really need to start over with compuers.
> The x86 still has the old 8086 op codes, and some of the memory addr 
> restrictions. Thats why if a Mac and PC of equal speed are set to do 
> the same 
> task that the Mac will get done first.
> 
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