[Pc_Support] RE: i586 vs. i686? -- i586 is _only_ for _genuine_, original P5 (Pentium/MMX)

[Bryan J. Smith <b.j.smith at ieee.org>]

From: Damien McKenna <dmckenna at thelimucompany.com>
> i586 is the Pentium, Pentium MMX and K5 chips.
> i686 is the Pentium Pro and anything based off it, including the Pentium
> 2, Pentium 3, Pentium IV, K6, Athlon, etc.
> Anyone else want to divulge some details on compatibility between them?

Alan Cox and I discussed this on the Fedora Development list last year.
And it just came up on the CentOS yesterday.
I made people aware that you should normally _never_ build for i586
_except_ for _true_, _original_ Pentium or Pentium MMX.

It's more than the fact that there is no guarantee that a clone is
i586 ISA compatible, but i586 optmizations are _detrimental_ to
most processors, _including_ Intel's own Pentium Pro, II, III and 4.

[ Correction in some posts, I used "--mopt" when I meant "--mtune" ]

List of i486 and i686 ISA compatible architectures (1/3rd from top):  
http://lists.centos.org/pipermail/centos/2005-June/007486.html  

Red Hat's stance (both FC and RHEL) on i586:  
http://lists.centos.org/pipermail/centos/2005-June/007510.html  

i586 marketshare and there is _no_, true "i586 clone":  
http://lists.centos.org/pipermail/centos/2005-June/007514.html  

More commentary on i586 v. i686 cores and optimizations:  
http://lists.centos.org/pipermail/centos/2005-June/007516.html  

More analysis of Red Hat FC v. RHEL and architecture support:  
http://lists.centos.org/pipermail/centos/2005-June/007532.html

Noting 500MHz+ i486 cores exist, and x86/PAE36 will still live:  
http://lists.centos.org/pipermail/centos/2005-June/007538.html  

Tangent on the future of OOE/RR/multi-core -> virtual-cores:  
http://lists.centos.org/pipermail/centos/2005-June/007544.html  

Cyrix/IDT/ViA on "cmov" which is optional in i686, but GCC requires.
Also a "breakdown" of what arch/tune do what to what processors:  
http://lists.centos.org/pipermail/centos/2005-June/007549.html  

Does rpmbuild --target=i386 turn into gcc --march=i486?  
http://lists.centos.org/pipermail/centos/2005-June/007552.html  
http://lists.centos.org/pipermail/centos/2005-June/007553.html  




--
Bryan J. Smith   mailto:b.j.smith at ieee.org