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Old 08-26-2005, 01:33 PM   #1
DJOtaku
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i386 kernel vs i686 does it matter?


According to /proc/cpuinfo I have

Pentium III (Copermine) 597.429 Mhz processor

When I installed Fedora Core 3 (it's been upgraded to Core 4), I just installed as usual and used the system.

One day I typed yum list to see which packages I hadn't installed and I was shocked to see kernel there - how could I have not installed the kernel?

Now, I haven't updated the kernel since the last time one came out for FC4, which was around 15 July, but here's what I think I remember from that time.

When I did yum update kernel - the arch was i386

When I did yum list - the kernel arch was i686

So, obviously I'm running the 386 kernel. But I'm running (as far as I know) a 686 machine. Does it matter? If I switched to the other kernel what would be the benefits/downsides?

Thanks,
 
Old 08-26-2005, 01:58 PM   #2
Half_Elf
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The 386 kernel will run on any intel 386 cpu and earlier (read : _everything_). 686 kernel will run on any intel 686 computer (P3, P4, AMD k6 and up). The i686 one should be faster, as it uses machine instruction (assembly code) that are unknown to 386, 486 and 586. However it breaks backware compatibility, that's why they give you the choice
 
Old 08-26-2005, 02:00 PM   #3
DJOtaku
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so if I install 686 kernel do I lose [the ability to run] all of my 386 programs?

Last edited by DJOtaku; 08-26-2005 at 02:04 PM.
 
Old 08-26-2005, 02:13 PM   #4
Half_Elf
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of course not. Only the kernel will be optimized. So the _kernel_ may be faster (if you ever notice a change) but it won't touch any installed program.

In linux world, you can either compile from source or to use precompiled package (rpm, deb, etc...). Some options exists in compiler to optimize code for newer processor, so when you make a package from a source code, you have to choice to enable, or to do not enable, the optimization. Usually it's a good idea (usually because sometime it is worst) but as I said, older cpu won't be able to use this (or worst : will crash randomly!).

In your case, the guy that make this 686 rpm decided to use optimization and the one that make the 386 one decided to not. That's all.
 
Old 08-26-2005, 02:19 PM   #5
DJOtaku
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Thanks for that clarification. Although I doubt it makes a huge difference on a new machine, with only 600 Mhz I'd like to get every little speed boost possible, especially at the kernel level.

I think I'll be installing that sucker today.
 
  


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