It appears you are in AMDAHCI mode. Check out this thread Avoid AMD AHCI driver at all costs - AnandTech Forums . I have found that MSAHCI performs better in your system. To check your transfer mode (sata 300 or sata 600) run CrystalDiskInfo program. You should be getting 400+ reads and 200+ MB/sec writes on that drive.
To verify drivers, go to Device Manager and look under the IDE driver and see what is installed. Uninstall the AMDSATA driver, restart your computer and let the system re-install MSAHCI drivers. I'm sure your drive will perform better! Good luck.