Run-Time Abstraction Services

Run-Time Abstraction Services (RTAS) is run-time firmware that provides abstraction to the operating systems running on IBM System i and IBM System p computers.

It contrasts with Open Firmware, in that the latter is usually used only during boot, while RTAS is used during run-time.

Later it was renamed to Open Power Abstraction Layer (OPAL), and it's stored in a PNOR (platform NOR) flash memory.

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