Edit 2/11/2013: Due to the date of this testing and the fact that this question still comes up fairly often, we have decided to revisit this topic with more modern hardware in our SATA 3Gb/s vs. 6Gb/s Cable Performance (Revisited) article. Check it out to see if the results are any different using newer hardware and cables.
In the offical SATA-IO document "Fast Just Got Faster: SATA 6Gb/s", the following is stated:
The same cables and connectors used for current SATA implementations can be used to connect SATA 6Gb/s devices. SATA-IO recommends utilizing quality components to ensure data integrity and robust operation at the fast 6Gb/s transfer rate. Cables already at the threshold of 3Gb/s operating margins may experience lower performance than expected at 6Gb/s due to an increased number of resends.
In other words, as long as you are not using cheap knock-off cables there should not be any difference. We prefer to have empirical data to back up these types of claims however, so we decided to compare a set of supposed SATA 3Gb/s cables against a SATA 6Gb/s cable.
Before running the speed tests, we cut open a set of cables to see if we could find any design differences. The big things to look for at the number of wires and the gauge (size) of the wires.
In the pictures, the sleeved wires are all the signal wires, and the unsleeved are the ground wires. You can see that all the cables have the same gauge of signal wire, although the Asus SATA 6Gb/s and the Intel SATA 3Gb/s both have an additional ground wire. This is not for performance reasons, but simply due to the design of the cable. Instead of having the cable in one piece, those two cables are more like two separate cables fused together. This should not have any effect on performance, which hopefully our speed tests will verify.
To compare the speeds for each cable, we configured our test hard drive as a secondary storage drive and ran the benchmarks with each separate cable. We used a very fast SSD SATA 6Gb/s drive on a SATA 6Gb/s port, so any loss of speed should quickly become evident. The benchmark we used was CrystalDiskMark.
|Asus P8P67 Pro
|Intel P67 SATA 6Gb/s
|2x Kingston ValueRAM DDR3-1333 2GB
|Intel 2500K Quad Core 3.3GHz
|Intel SSD 510 250GB SATA 6GB/s
|Windows 7 Ultimate 64-bit
With all that said, lets take a look at the actual performance of each cable. All results are in MB/s.
|Asus SATA 6Gb/s (Black)
|Asus SATA 3Gb/s (Red)
|Asus SATA 3Gb/s (Black)
|Intel SATA 3Gb/s (Blue)
|Random Read 512KB
|Random Write 512KB
|Random Read 4KB (QD=1)
|Random Write 4KB (QD=1)
|Random Read 4KB (QD=32)
|Random Write 4KB (QD=32)
From these results, we can pretty conclusively determine that all of these cables are running at the full SATA 6Gb/s speeds. There are of course some minor differences between the results, but they are all well within normal testing variations.
In conclusion, our testing has agreed 100% with SATA-IO's statement that SATA 3Gb/s cables will work perfectly fine with SATA 6Gb/s drives. This wasn't much of a surprise to us, but it is always nice to have hard data backing up a claim.