FC5 i386 or x86_64 which way to go?

[Alphax]

David Lloyd wrote:
> Allan,
> 
>> The main reason I gave the x86_64 any thought at all is to the fact that 
>> it seems silly (to me) to still downloading an OS for an i386, when it 
>> has been outdated for (I think) more than a decade. That begs the 
>> question: How likely is it that a 386 could run any version of fedora 
>> core, let alone 5?
> 
> The vast majority of chips are compatible with the i386 instruction set,
> which means that if you are making binaries it's a good bet that if you
> use that instruction set your binary or library will be compatible on
> most computers that are compatible with an i386 instruction set.
> 
> For example, at my work, our PC Compatible mixture includes AMD Durons,
> AMD Athlongs, Pentium IVs and a Pentium M. We compiled a Gentoo
> installation of Apache and PHP5 on the Pentium IV with the architecture
> specified to be a Pentium IV. We then moved said binaries to one of the
> AMD Durons and it mostly worked...
> 
> ...until one obscure part of our code caused PHP5 and/or Apache to core
> dump...
> 

man gcc:

Pentium 4 has MMX, SSE, SSE2 support.

Duron has... err... pattern not found. Hrm.

Apparantly[1] Duron was the budget version of the Athlon. Depending on
which revision, it may have been equivalent to the original Athlon or an
Athlon XP. Back to man gcc:

Athlon has MMX, 3dNOW!, enchanced 3dNOW!, partial SSE support.
Athlon XP has MMX, 3dNOW!, enchanced 3dNOW!, full SSE support.

So, if you compile on/for a Pentium 4, it will use:

- i386 instructions
- MMX instructions
- SSE instructions
- SSE2 instructions

Try and run the binaries on a Duron.

- i386 instructions - no problem.
- MMX instructions - no problem.
- SSE instructions - may or may not be a problem depending on the
hardware revision.
- SSE2 instructions - definite problem.

... what does this all mean for someone who knows nothing about hardware?

Well, imagine you take a driver who has only ever driven a car with an
automatic gearbox and put them into a car with a manual gearbox. Bad
Things are going to happen. Some of the basics are the same (steering,
accelerator, etc.) but others are different. Like changing gears...

HTH.

[1] http://en.wikipedia.org/wiki/Duron
-- 
                Alphax
        Death to all fanatics!
  Down with categorical imperative!
OpenPGP key: http://tinyurl.com/lvq4g

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