If i have a sata3 motherboard does this mean i need a sata3 hard drive

Welcome to Tom's Forum!  

On a HDD I do NOT recommend using the SATA3 ports, but IF they're all SATA3 then verify that the HDD if using with a SATA3 'Interface' that it has the latest FIRMWARE installed. Often the Western Digital SATA3 HDD are problematic on SATA3 ports.

To answer your question, no HDD is faster than 120MB/s-150MB/s or in other words 1/2 the SATA2 'Interface' speed. No, SATA3 HDD 'Interface' is NOT required the SATA3 Interface is fully backwards compatible.

You'll have less issues with a SATA2 HDD and will not suffer any speed loss.

I have Wdc black Sata 2 7000 rpm speed 3mb/s installed in my MB sata 3 port , No issue and problem till now, performance same result WEI score at 5.9 . It's mean no problem with HDD sata2 installed MB sata3 port.

Hard drives can't run fast enough to justify using SATA III ports for speed, but they can use them for the extended capabilities (eg: NCQ). So some hard drives are marked as SATA III, and some aren't.

Even so, you can generally plug SATA II hard drives into SATA III ports without problems, and you can plug SATA III hard drives into SATA II ports without problems.

Most new motherboards have a mix of ports, some SATA III, some SATA II. If you have the option, then use the SATA II ports for your SATA II hard drive. The manual will tell you which is which.

NCQ {Native Command Queuing} is used by AHCI, both SATA2 or SATA3 can use this feature, and I do recommend AHCI. Just verify the 'Start' values = 0 in the registry; Windows -> http://support.microsoft.com/kb/922976