Do all certified systems support full cpuscaling in Red Hat Enterprise Linux 5?

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No, hardware must meet certain requirements to support cpuscaling in Red Hat Enterprise Linux 5. For Intel processor, it should support EIST(Enhanced Intel SpeedStep), for AMD processor, it should support PowerNow or Cool'n'Quiet.

In addition to CPU support, the system BIOS must also support full virtualization. Please contact the system vendor to determine if the BIOS supports cpuscaling.

Note: that if this Knowledgebase article was linked from a system listing on the Red Hat Hardware Catalog, the system in question does not support cpuscaling.