Going 64 bit

Bryan Sant bryan.sant at gmail.com
Sat Jan 27 15:54:31 MST 2007


On 1/26/07, Michael Torrie <torriem at chem.byu.edu> wrote:
> Sure, but this doesn't matter anymore.  Let's face it.  They used to say
> RISC was the wave of the future.  And they were partially right.  But
> now the gap between RISC and CISC is narrowed significantly.  Most x86
> chips (AMD or Intel) are really RISC cores with a microcode translator
> that converts the more compact CISC instruction sequences into RISC
> microcode where it is pipelined, reordered, etc.  This gives all the
> advantages of RISC without having to actually force RISC ISA on the
> compilers and programmers.  In effect this means the RISC never really
> panned out like everyone thought it would at the higher level.  x86_64
> has the advantage of having about twice the code density of a 64-bit
> instruction word 64-bit RISC processor.  And even though memory and disk
> space is cheap, this higher density pays off in terms of increased cache
> performance.
>
> On the flip side, the x86 ISA, 64-bit or not, is old, bloated, and full
> of strange anachronisms like memory segmentation and "real mode"
> garbage.  It's likely you can still boot MS-DOS on an AMD 64-bit
> machine.  However the x86_64 extensions do give us a path forward and
> perhaps future cpus can drop support for older things like real mode, 16
> and 32-bit instructions.  Who knows.
>
> Michael

+1 Insightful.



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