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Old 03-15-2006, 07:00 PM   #1
Registered: Feb 2006
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Newbie question about kernel 686

Like the title of my post, i want to know, if it's possible, what's it's the good thing about the kernels 686

As far I know, they are kernels created to work better in machines that has a Pentium or ADM Kx and follow

It may be possible to me understand that, but, really, what is that this kernel improve in system which has this kind of processors?

If this question has been already treathed, sorry by the inconvinience.....

Thanks and bye
Old 03-15-2006, 07:09 PM   #2
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The basic idea has to do with instruction scheduling and instruction set.

You want to tell the compiler what kind of CPU you have so it knows how to schedule instructions efficiently. Some CPUs have 2ALU units and 2FPU units, some have 3/3 some have 4/3, etc. The idea is you want the compiler to reorder instructions so as to mix the propper number of ALU and FPU instructions. If the order was 32 fpu and then 32 ALU later, you would only be using half your CPUs processing units. If you could mix those same instructions into 8 4+4 batches, you could better utilize the CPU. The real story is much more complex, but you get the idea. This is why you would want to choose the closest match to your actual processor.

Also, some CPUs have support for additional instruction sets like MMX, SSE, 3DNow, etc. I think there have even been changes in the standard x86 line (386,486,686,etc). If your processor supports these instructions, it would be nice to tell the kernel (and compiler) so it could take advantage of them. I'm not sure what exactly i686 includes, but again, you get the idea, and you want to choose the closest match to your actual CPU.

Last edited by visaris; 03-15-2006 at 07:12 PM.
Old 03-15-2006, 07:46 PM   #3
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Each one is a newer instruction set, i686 contains instructions that i586 doesn't support, and i586 contains things that i486 didn't support, etc. i686 is Pentium Pro and better; almost all x86 computers you can find today are i686 or above
Old 03-15-2006, 08:19 PM   #4
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look here. Myself and others posted the diff between 386/486/etc

there are lots of posts here about it though. take a look around
Old 03-15-2006, 08:23 PM   #5
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Well, interesting note visaris, like you said, I got the point.....

Thanks to you also spooon.

So, the basicly idea of this improvement, is to help the kernel to satisface the instructions suported by the processor, but, this affect the packages which install using 386? or i'm complity lost and has nothing to do with this? jajaja

I mean, if I have a kernel 686, and install a package which comes in 386, this package is recompiled to reach the 686 structure or simply, run using only 386 support?

Thanks for the answers

Old 03-15-2006, 09:08 PM   #6
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The i386 packages have been compiled to run on any 386 (or higher) processor so they won't have the additional instructions (MMX etc.) supported on 586 or 686 processors. What processor the kernel was compiled for does not make any difference to userland applications (other than a snappier kernel will make the system as a whole feel more responsive).
Old 03-16-2006, 05:34 PM   #7
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Thanks for the answers, I understand now

I'm new in this linux world so I'll be asking for much time jejeje

Hopefully, some day I can be a help.....



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