The USB Implementers Forum introduced the final USB 3.0 specification at the end of 2008. As you can imagine, the new standard once again will accelerate throughput, and although the speed bump isn’t as significant as 40x when USB 1.1 was replaced by USB 2.0, there still is a 10x increase in bandwidth. USB 3.0 is specified to run at 5 Gbit/s maximum speed. However, this increase is still great enough to offer almost twice the bandwidth of today’s Serial ATA standard (3 Gbit/s gross bandwidth).
Is 5 Gbit/s Too Much?
Every enthusiast will confirm USB 2.0 being one of the main bottlenecks in modern PCs and notebooks, as the peak net throughput typically lies between 30 and 35 MB/s. However, 3.5” desktop hard drives typically reach far more than 100 MB/s today (there even is a 2.5” notebook hard drive that can deliver this kind of throughput). Fast flash SSDs break 200 MB/s. Still, 5 Gbit/s (or 5,120 Mbit/s) equal 640 MB/s gross bandwidth.
While we don’t expect hard drives to get anywhere near 600 MB/s within the predictable future, next-generation flash SSDs might surpass that number in only a few year's time. And this type of throughput is getting more and more important as increasing amounts of data also extend the time required to run backups. The faster your storage, the easier it is to maintain short backup windows.
Headroom For The Future
It isn’t uncommon for digital camcorders to store multiple gigabytes of video data. Moreover, the rising prevalence of HD-capable cameras will require larger and faster storage devices to handle the increasing amount of data. USB 2.0 already takes quite a while to transfer double-digit gigabyte quantities of data to a PC for editing purposes. The USB-IF shares the opinion that bandwidth remains of principle importance and expects USB 3.0 to be capable of handling all consumer devices within the next five years.
In an effort to ensure reliable data transfers, USB 3.0 utilizes an 8b/10b encoding, which is also being used by Serial ATA. 10-bit words are represented in a 10-bit encoding, which results in more reliable transfer at the expense of useable bandwidth. Hence the conversion from bits to bytes has to happen at 10:1 instead at 8:1.
|Specification/Interface||Nominal Throughput (Mbit/s)||Nominal Throughput (MByte/s)|
|SATA / eSATA 150||1,500||150*|
|SATA / eSATA 300||3,000||300*|
* 8b/10b Encoding