Query about sata cable

I don't think that there is a serious difference between the cables and either way, no hard drive that you'd have is fast enough to make use of SATA3 anyway. Supporting something and being able to make use of it are two different things. Fr example, a Radeon 7750 supports PCIe 3.0, but a PCIe 2.0 x4 slot would hardly impact performance on that card compared to a PCIe 3.0 x16 slot that has about eight times higher PCIe bandwidth. Hard drives simply tend to not saturate SATA 2 except maybe for their cache, but even then, it doesn't make much of a difference. SATA3 support on hard drives is kinda gimmicky as far as I know.

Thanks for clear my confusion.

You're welcome.

Really, SATA3 is currently only important for most consumers on drives such as high-performance SSDs because they can go much faster than the sub 300MB/s that SATA2 allows. Hard drives tend to max out between 100MB/s and 200MB/s and usually can't get even that high except in very specific uses, so increasing the SATA bandwidth doesn't matter becausing you're increasing something that isn't a bottle-neck. It'd take a hard drive such as a very high speed 4TB 10KRPM or 15KRPM hard drive to saturate SATA2 and there simply aren't such drives for consumers, if any exist at all.