First Look at USB 3 Performance

Hands on with USB 3.0

It’s incredible to think of how ubiquitous the humble USB port has become since its first release in early 1996, when the port was designed specifically to simplify connecting the increasing array of peripherals available for personal computers. At one point, the USB port was subjected to derision as Windows 98 didn’t support it – you had to install a driver for your USB device from a floppy disk in order to use it. Jump forward fifteen years and almost every new electronic device is powered or connected via USB, with faster competitors such as FireWire and eSATA unable to find a purchase in face of USB’s all-conquering plug and play user friendliness.

The simplicity and universal adoption of USB as a means of connecting a device to a PC has seen the rise of technologies we now take for granted: flash drives, MP3 players, digital cameras and external hard disk drives. However, USB has struggled to deliver the ever faster transfer speeds consumers have demanded.

The original USB spec allowed for theoretical maximum transfer rates of 12Mb/sec (1.5MB/sec). USB 2 dramatically improved things, with a jump to a theoretical maximum of 480Mb/sec (60MB/sec) shared between all connected devices. However, device controller limitations meant such speeds were rarely, if ever, attainable.

First Look at USB 3 Performance USB 3.0 - It's over 5000! (bit/s) First Look at USB 3 Performance USB 3.0 - It's over 5000! (bit/s)
Click to enlarge- the first USB 3.0 devices are now reaching retailers

The arrival of USB 3 is a pretty big deal then - a major update to the way that we interact with our PCs and our increasing array of mobile devices. With the USB 3 specification finalised over a year ago we’ve known for a while the potential of USB 3. With claims of a maximum theoretical speed of 5Gb/sec, or 625MB/sec, matching the potential speed of SATA 6Gbps. However, this figure is the absolute maximum possible via USB 3’s ‘super speed’ bus – a feature that no current device supports. We therefore really only expect a true maximum speed of 4Gb/sec from USB 3 at present, and even then, real-world transfer speeds will be slower still, around the 3Gb/sec mark (375MB/sec). That’s still a huge step up from the pedestrian speeds of USB 2, which rarely exceeded 40MB/sec.

First Look at USB 3 Performance USB 3.0 - It's over 5000! (bit/s) First Look at USB 3 Performance USB 3.0 - It's over 5000! (bit/s)
Click to enlarge - The difference between USB 3.0 and and 2.0 is subtle, but significant

Transfer rates aside, USB 3 is also physically different to USB 2, to the point that just looking at the thickness of the cables is enough to give it away. This is because USB 3 adds fives new data lanes to the existing USB 2’s four, allowing for simultaneous upload and download of data; USB 2 shared the two data lines, leading to abysmal simultaneous read/write performance. This makes a USB 3 cable noticeably thicker than a USB 2 wire.