Sorry! I read port 5 in your post and forgot that the ICH9R has 6 ports not 4. Because of that I thought that your Plextor is on the Taiwanese controller. Sorry for that!
But I still have to add, that the PX-755SA is NOT a “native SATA” drive. It has a MARVELL IDE-SATA bridge-chip. But thanks to your post, I know now that the MARVELL chip works with AHCI mode enabled. And that’s a great thing. I now start to think that every ide-sata bridge-chip works with AHCI enabled. I’m not sure, but I think, that every SATA specifcation includes AHCI. AHCI (and NCQ) just weren’t available with HDD at the beginning, because the first ones weren’t “native SATA” and after the bridge the IDE drive could not handle AHCI/NCQ. It wasn’t because the bridge-chips were early SATA specifications I guess.
GIGABYTE BIOS: The “SATA Port0-3 Native Mode” sets “Native IDE” or “Legacy IDE”. It does NOT set “Native SATA” or some else SATA. That whole setting is irrelevant. It MUST be set to “Enabled”, because “Legacy IDE” is for Win98 only, but that is unimportant, because naturally as soon as you set “SATA RAID/AHCI Mode” from “Disabled” (which is IDE compatible SATA) to “AHCI”, the “SATA Port0-3 Native Mode” setting loses its function.
Thanks for renaming the BIOS setting to “SATA Port0-5 Native Mode” with the new P35/ICH9R boards.
I did some research myself and now I know it, so if other people are wondering as well: Every drive, that has two different chipset versions for PATA and SATA is a “native SATA” drive. The LITEONs and SAMSUNGS have the MT1898 for PATA and the MT1899 for SATA. Same case with Optiarcs and Pioneers and two different NEC chipsets.