Red Hat Knowledgebase

The AMD64 or Opteron CPU self-identifies as an Athlon in 32-bit mode, so you get the Athlon kernel. The IA32E or EM64T chip identifies as a flavor of Xeon with Physical Address Extentions (PAE) support in 32-bit mode, so you get the hugemem kernel. Red Hat did this because there was a desire to make sure that the customer understood the performance implications involved with using the hugemem kernel.

Also, note that the 32 bit SMP kernel has PAE enabled and has support for up to 16GB of RAM.

For an overview of the various kernels in Red Hat Enterprise Linux 3 consult the Red Hat Documentation found online: Red Hat Enterprise Linux 3: System Administration Guide, Overview of Kernel Packages.