SATA 3 is the latest and fastest standard for hard drives and solid state drives. But what is the actual speed of SATA 3? The SATA 3 specification defines a maximum data transfer rate of 6 Gbps. In reality, most hard drives and solid state drives are capable of operating at much faster speeds. The fastest SATA 3 drives can reach up to 10 Gbps. ..
When researching about the speed of SATA 3, the “stated speed” and the “actual result” are noticeably different, so what exactly is going on? Today’s SuperUser Q&A posts helps a curious reader understand more about how SATA 3 works.
Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-driven grouping of Q&A web sites.
Photo courtesy of GiocoVisione (Flickr).
The Question
SuperUser reader Space Ghost wants to know what the actual speed of SATA 3 is:
What is the actual speed of SATA 3?
The Answer
SuperUser contributor MariusMatutiae has the answer for us:
Have something to add to the explanation? Sound off in the comments. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion thread here.
While data is actually sent at 6 Gb/s, it is encoded to counteract two common defects in telecommunications, DC Bias and Clock Recovery. This is often accomplished using a specific coding algorithm called 8b/10b Encoding. It is not the only encoding algorithm which has been devised to this end (there is also a Manchester encoding), but it has become the de facto standard for SATA data transfer.
In 8b/10b encoding, eight bits of signal are replaced by 10 bits of (signal + code). This means that, out of the 6 Gb the channel sends in a second, only 8/10 (4/5) are signal. 4/5’s of 6 Gb is 4.8 Gb, which in turn equals 600 MB. This is what degrades the 6 Gb/s channel into a mere(?) 600 MB/s channel.
The advantages obtained by compensating for DC bias and allowing for Clock Recovery more than compensate for this slight degradation.
