Run-Time Abstraction Services

Run-Time Abstraction Services is run-time firmware that provides abstraction to some operating systems. These include those 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, and it's stored in a PNOR flash memory.
Ppc64-diag, libservicelog, servicelog, and powerpc-utils packages can be used to diagnose RTAS events.