From: Johnny Hughes <mailing-lists@xxxxxxxxxxxx>
> Right ... but in a software capacity we are also talking about pentium,
> pentium mmx, cyrix i686, amd k6, via c3 that use i586 packages.
No! You _never_ want anything but a _true_ Pentium or Pentium MMX
using i586. i586 ISA and/or optimization are _not_ good for anything
but those 2 chips.
You want to use i686 for AMD K6, Cyrix M2 and Via C3.
You want to use i486 for AMD K5 and Cyrix 6x86/M1.
This is one of the most misunderstood details in the user world.
> CentOS is trying to provide limited support for them. This support
> doesn't in any way affect other packages like glibc.i686 or the i686
> kernels ... In case someone might be concerned about a CentOS / RHEL
> divergence. The i586 packages are only installed on machines that have
> i586 processors ...
I understand that. But the point you are missing is that there are
_only_2_ "i586 ISA" processors: Pentium and Pentium MMX
Do not confuse "i586 class" with "i586 ISA."
I appreciate that CentOS offers these added processors, since Red Hat
does not consider it their bother -- whether they only ship i486 and
i686, or just i686 now (since all designs of the mid-to-late '90s are
i686 ISA).
> if you have i686 then that is what is installed on your machine.
I understand.
> Red Hat did seem open to at least reviewing a patch to the glibc
> package that provides i586 support if we get it working.
And that's great. But I'm sure the marketshare is why they didn't
do it themselves.
Right now, the market is:
i686 ISA compatible > i486 ISA compatible > i586 ISA compatible
And it's been like that for awhile. But even before then, it's
_always_ been:
i486 ISA compatible > i586 ISA compatible
i586 is not recommended, even if i686 ISA compatible typically means
i586 is supported. It's just rather poor performing, and you can
occassionally run into a serious instruction issue (especially with
early i686 clones that did i686 fine, but not always i586).
There is _no_ "i586 clone" -- no one would purposely clone the
Pentium's instruction set because it was quickly superceded by
i686 for good reasons. Unfortunately, Intel took forever to get
past its Pentium Pro offering, which was never designed for
consumers, and finally offer an i686 for consumers in the Pentium II.
Hence why i686 clones like the AMD K6 actually pre-date much of
the widespread consumer adoption of an i686 from Intel itself because
the consumer chip didn't hit for years after its first ISA.
idSoftware always had excellent commentary on i586 v. i686, largely
because they found some of the best hacks for i586 to get around
many of its ALU design flaws.
--
Bryan J. Smith mailto:b.j.smith@xxxxxxxx
