What is IBM Power 7 Systems compatibility mode?

Issue

• What is IBM Power 7 Systems compatibility mode?

Environment

• IBM Power Systems server based on POWER 7 processor.

• Operating system based on the Linux kernel.

Resolution

• When running Linux on a POWER 7 system, users will sometimes see that the system is running in a compatibility mode. Whether the system runs in native mode or compatibility mode is determined by which kernel is running on the system. The Linux kernel contains code that defines what capabilities the kernel supports. When the kernel is booted it will report its capabilities to Open Firmware. Based on the capabilities reported, the Open Firmware will configure hardware settings accordingly, and the machine may be put into a compatibility mode.
• 'Compatibility mode' simply means that the POWER 7 processor will act as though it were a POWER 6 processor.
• As applied to Red Hat Enterprise Linux, in practical terms this means that POWER 7 systems are fully supported in compatibility mode when running RHEL 5.5 or later. POWER 7 systems are fully supported in native mode starting with RHEL 6.