[Gllug] 64bit linux / debian

[Richard Jones]

On Tue, Jul 08, 2003 at 01:03:30AM +0100, Ian Norton wrote:
> are IA-64 and X86-64 compatible? or is IA-64 totally different to the x86
> architecture?

IA-64 is a totally new architecture, based on a technology known as
VLIW. VLIW requires very smart compilers to schedule code optimally,
versus the current situation where dumb code is optimised at run time
by the processor. The theory is that by moving the work to the
compiler, you will simplify the CPU, and thus make it faster. In
practice the IA-64 architecture is quite baroque, and compilers aren't
as smart as they are supposed to be, and so the processor is much
slower and the compilers aren't very good. It is widely regarded as a
huge mistake (for Intel), but you never know ...

x86-64 is another hack on top of the x86 architecture ("IA-32") which
adds a 64 bit address & data mode to the existing 32 bit
architecture. Note that the existing x86 32 bit architecture is a hack
on top of the original 16 bit architecture. This doesn't sound too
good, and in theoretical terms it would be much better to just move to
a new architecture. However since 99% of the world's code is compiled
for the x86, and since applications matter, extending the architecture
makes more sense. Also modern processors don't run x86-32 or x86-64
code directly anyway, instead they translate it to an internal RISC
format which then runs much faster. It looks like x86-64 is going to
be better, cheaper and faster than the Intel offering, but again you
never know ...

Rich.

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