Sata1 controller mode on desktop PC HPp6345a

Hi,

I am new to this new BIOS setting for SATA1 controller mode (AHCI or RAID?).
My desktop PC is HP p6345a and the default SATA1 controller mode is RAID.
The hard disk is already busted and need to replace it and reinstall the OS by using HP recovery media.

My question is do I need to set the SATA1 controller mode to default whihc is RAID or change it to AHC1?
Also may I add that I am planning to backup my computer on an external hard drive after I the recovery.

Please help.

Regards,
Neggie