USB 3.0 Basics And Applications
The USB 3.0 standard is also referred to as SuperSpeed USB. This was necessary because USB 2.0 was promoted as High-Speed USB several years ago. Here is an overview on the nominal throughput of all popular peripheral interfaces:
| Throughput Overview | ||
|---|---|---|
| Specification/Interface | Nominal Throughput (Mb/s) | Nominal Throughput (Mb/s) |
| USB 1.x | 1.5 | 0.19 |
| USB 1.x | 12 | 1.5 |
| USB 2.0 | 480 | 60 |
| USB 3.0 | 5,000 | 500* |
| FireWire 400 | 400 | 50 |
| FireWire 800 | 800 | 80* |
| SATA / eSATA 1.5 Gb/s | 1,500 | 150* |
| SATA / eSATA 3 Gb/s | 3,000 | 300* |
* 8b/10b Encoding
While the connectors for USB 1.1 and USB 2.0 are identical, USB 3.0 requires nine, rather than only four, wires. The five additional wires are necessary for SDP transmission based on shielded differential pairs of wires. USB 3.0 greatly resembles SATA, providing data both in upstream and downstream directions.
Fortunately, USB 3.0 is backward compatible with USB 2.0, as the five additional contacts are placed deeply within the connector. Plug a USB 3.0 connector into a USB 3.0 port and you’ll get the 5 Gb/s connect. Inserting the connector only half-way or attaching a USB 2.0 device will result in 480 Mb/s USB 2.0 speed. USB 3.0 also supports 900 mA per port, rather than USB 2.0’s 500 mA. This is a blessing for portable storage devices that require a bit more power to operate. With USB 2.0, some devices would only work with Y-type cables to access power from two USB 2.0 ports.
USB 3.0 Applications
The most obvious candidates for USB 3.0 are external and portable storage products, such as hard drives or flash-based thumb drives. All of these can immediately benefit because the 35 MB/s bottleneck vanishes. Even low-cost hard drives reach 50 MB/s today, 2.5” mobile hard drives are crossing the 100 MB/s line, and 3.5” desktop hard drives are somewhere between 100 and 150 MB/s these days. Clearly, USB 3.0 allows all conventional hard drives to operate without throughput bottlenecks. Fast USB 3.0 drives might also be interesting for mobile operating system installations, such as a maintenance system on a thumb drive.
