We recently made a change in Fedora kernel packaging, to drop the regular 686 kernels. As of Fedora 11, the only 32-bit kernels built are ‘586’ and ‘686-PAE’ (and their -debug variants).
In F11, at install-time, Anaconda will install the PAE kernel if the CPU is capable of using it, and otherwise, will fall back to the 586 kernel. (Users upgrading with yum will see a 686->586 transition unless they are already using the -PAE flavour)
Both kernels actually have instruction scheduling optimised for 686 (Using gcc’s -mtune=generic, which optimises for the popular CPUs of the time).
The actual differences between the two builds:
- Uses only up to the i586 ISA
- Supports up to 4GB of RAM.
- Will use segment limits to approximate NX.
- Uses the 686 ISA including CMOV.
- Uses 3-level page-tables allowing >4GB RAM.
- Where possible, uses hardware NX instead of segment limits. (faster)
- Has Xen virtualisation enabled.
Processors that will need to use the 586 kernel include..
- all AMD CPUs prior to the Athlon
- Intel Pentiums prior to the Pentium Pro
- Some subset of Intel Pentium M’s (These are the only ‘modern’ CPUs)
- All Cyrix and Transmeta
- All VIA prior to Esther