Okay, so I'm receiving the last part of my computer tomorrow (which means I finally get to put it all together yay!) and reading through the MB manual I'm unsure about what to set the southbridges SATA ports to. I will have the option of Legacy(PATA), ACHI or RAID. I will be using a SATA hard drive and optical. My question is which one should I use for the best performance?

RAID is the obvious choice for performance. You'll need to configure your drives to use it though (RAID requires more than one drive, which work together in tandem)

AHCI enables SATA-specific features which can theoretically increase performance; however, it can actually slow down most of the drives out there. The reason is many SATA drives have been merely IDE drives with a SATA interface strapped to them. For hard drives that support the SATA-specific feature set, things like NCQ *may* improve performance, depending on how you use your computer.

When all is said and done though, I can't imagine noticing the difference between IDE and AHCI. Even RAID 0 is tough to notice in normal computer use.

Will Raid only work with one hard drive? I don't know if it matters but the hard drive will be a Caviar Black 1tb, I remember reading somewhere that ACHI might screw up your optical sata drive, although I'm not sure... so Raid is the right way to go?

RAID by definition uses more than one drive. It's purpose is either improved performance, redundancy or both.

So I can use just one drive on raid?

The answer for your purposes is no.

*Technically*, you can use one drive on a RAID controller, but there's really no benefit because it isn't actually a RAID. RAID = Redundant Array of Inexpensive Disks. To have an 'array' of anything, as you probably know, means you need more than one.

The reason RAID can be faster is that it will combine the performance of two or more drives. This array of drives share the work load and appear as only a single to the operating system (Windows). You'll commonly see RAID 0 used by performance-drive PC enthusiasts, since it is the fastest type of RAID.

Here's a relatively clear explanation:
http://www.acnc.com/04_01_00.html

raid-0 is the performance option and raid-1 the mirrored option.

however, even Microsoft does not recommend Raid for the boot disk.

Raid is intended for server system, not home use, client systems.

Microsoft also states they only reason they don't recommend RAID for system disks is increased data recovery complexity.

Aside from that, there is no argument against it except mediocre performance gains for multiples of cost.

I agree totally on both points, but that complexity is often fatal as proper backups are seldomly performed.

Quoted for truth... Sad but true.