PM2 is a power management feature. The info below originate from Western Digitals home page.
----------------------------------------------------------------------------------
The mode enables controlled spinup,
mainly used for server/workstation environments operating in multiple drive configurations.
IMPORTANT: PM2 mode requires a compatible BIOS that supports this feature. If PM2 is enabled and not supported by BIOS, the drive will not spin up and therefore will not be detected by the system.
---------------------------------------------------------------------------------
I've just ordered me a 500 GB Black Caviar disk...
/Anders - The Sourcerer