I just picked up a Samsung 840 Pro 256GB SSD from NewEgg and plopped it in my box. I connected it to one of the two SATA3 sockets on my Gigabyte 790XTA-UD4 motherboard.
I fired up the box, let the Samsung Magician software configure some Windows settings (for performance, it told me), restarted, then did their performance benchmark. The number came out quite a bit lower than I would have expected.
So I poked around a bit more and realized that I hadn't configured the SATA3 ports to run in AHCI mode. So I first checked the registry to see if Windows (7 64-Bit) was configured for AHCI. The Start key-value-pair had a value of 0 as people said it should so I assumed it was. I then backed out to the BIOS and configured the SATA3 ports to use AHCI and rebooted. Still poor performance.
That is when I noticed the "Disk Drive" screen on Samsung Magician which informed me that my drive was not using SATA3. "I must not have installed drivers," I thought to myself. So I popped open Device Manager and looked. It was using the Windows default AHCI drivers. "Well surely we can do better than that." So I went to Gigabyte's website and downloaded the latest drivers for my board and installed those in place of
You can see the benchmarks, "Disk Drive" screen, and the information in Device Manager in this imgur album: http://imgur.com/a/ZdygY
Other (possibly) relevant information:
AMD Phenom II X4 2.8GHz
8 GB of RAM
Windows 7 64-Bit
Gigabyte 790XTA-UD4 motherboard
The SATA 600 ports (SATA 3) are provided by a Marvell controller. These controllers are known to give quite poor performance. Usually they aren't much faster than the SATA 300 ports provided by the chipset.
Intel designed the SB and IB chips with on chip SATA III controllers, which are lacking on the AMD Phenom series. The slower throughput is due to the added Marvel controller interpolating the data.