Why are there only i686 and i586 Version of glibc and kernel? -- i386 is still around
Bryan J. Smith
b.j.smith at ieee.org
Tue Jun 1 15:30:34 UTC 2004
Leonard den Ottolander wrote:
> This issue was discussed in the thread "Making NPTL the default for
> FC3, vanilla i386 support". Both i386s and i486s are already no longer
> supported since FC 1. Try running rpm on either of these CPUs and see
> it fail. See
> https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=103078 .
FYI, the original Cyrix 686 (M1?) was only i486 compatible. You had to go
with the 686"L" or M2 to get full i586 ISA compatibility.
Frankly, I don't think people recognize the _real_ reason for trying to
keep i386/486 ISA compatibility. It's not to support old systems, but to
support i386/486 ISA embedded microprocessor cores in all sorts of black
box solutions. These solutions have full desktops/GUIs far more than you
may think.
All it takes is one major black box vendors to adopt Fedora and we're
talking over a 1% marketshare.
GCC still pumps out i386 ISA code, while making other optimizations. So
anything that has a patch or otherwise that breaks this should be
revisited. So there is still a good reason to strive for i386/486 ISA.
> So if there is the intention of making the move to i486 as the minimum
> arch we could just as well make the jump to i586.
I would continue to favor i386 with i686 (Pentium Pro) optimizations.
i586 (Pentium) causes a lot of de-optimizations in newer processors, even
Intel's own. Why? Understand that about 80% of "Pentium optimizations"
were really "errata workarounds." The Pentium was the first superscalar
x86 design, and boy did it have some real muck-ups that had to be
compensated in software (like the ALU LOAD being 3x slower, which id
found it far faster to load via integers via the FPU instead).
--
Bryan J. Smith, E.I. -- b.j.smith at ieee.org
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