The first USB 3 external hard disk has arrived in the PC Pro Labs – a pre-production sample courtesy of our friends at Asus – and initial impressions are simply excellent.

The chart above may need a little explaining. The first two groups of results show how long it took, in seconds, to copy a folder of 3,000 small files, totalling 300MB in size, back and forth between a RAM disk and an external hard drive using various connections. The 650MB results are based on the same process using a single 650MB file.

The USB 2 and USB 3 figures were obtained by simply connecting the external drive first to a USB 2 port and then to a USB 3 one. The eSATA figures are from the A-Listed Iomega Professional External Hard Drive.

The results

As you can see, USB 3 left USB 2 comprehensively in the dust in every test. That’s no surprise: USB 2 has always been a bottleneck for external hard disks, with even “Hi-Speed” mode limiting transfer speeds to a theoretical maximum of 480Mb/sec. USB 3 adds a new “SuperSpeed” mode that increases the bandwidth by a whopping ten times, yielding greater throughput than a typical SATA connection and enabling external drives to communicate at full speed. In our real-world 650MB test, the external drive connected via USB 3 averaged sustained read and write rates of around 120MB/sec, beating even our eSATA unit.

Our 300MB test was a little less clear-cut: USB 3 raced past USB 2 as expected, but eSATA performed erratically. In the write test, eSATA was three times as fast as USB 3, but in the read test it was barely faster than USB 2. It seems the SATA interface makes better use of buffering than USB when it comes to writing files, but it doesn’t read files back so efficiently. Overall, if pressed as to whether USB 3 was better than eSATA, we’d have to say “mostly”.

The connector

One interesting aspect of USB 3 is that it brings a new connector — the first one since USB 1 was specified in 1996 that actually involves an electrical change, rather than simply being a different shape. Previous versions of USB have used four-pin connectors, but to enable “SuperSpeed” transfers, USB 3 devices use new eight-pin connectors.

The upgrade has been very thoughtfully implemented, though. You can still use a four-pin cable to hook up a USB 3 device to your PC — you’ll just be stuck at USB 2 speeds.

And if you have a USB 3 cable you can still plug it into a USB 2 socket on your PC: again, your device will simply fall back to USB 2 speeds.

The only thing you can’t do is plug a USB 3 cable into a USB 2 device. That’s because the new USB-B plug is physically larger than the old USB-B socket, to connect with the four extra pins which have been piggy-backed onto the top of the existing design (pictured).

The future

Will USB 3 catch on? Technically speaking, it’s hard to see why it wouldn’t. The performance benefits are simply unanswerable. Of course, not all USB devices will benefit, since things like printers and flash memory devices don’t saturate an existing USB 2 connection. But USB 3 ports and devices retain full compatibility with USB 2, so there’s really no reason not to switch.

(Indeed, despite what you may hear on this week’s PC Pro podcast, it appears that USB 3 even maintains support for USB 1.1 devices and ports.)

The transition may be slow, though. Neither Intel nor AMD yet supports USB 3 at the chipset level, so for now you’ll find it only on premium motherboards with dedicated third-party USB 3 controllers (such as the Asus P7P55D-E or the Gigabyte GA-P55A-UD3). If you want to add it to an existing system, you’ll need to invest in a PCI-E controller card. It’s safe to say that, with these as its only distribution channels, USB 3 isn’t going to flood the mainstream in the immediate future.

All the same, if USB 3 achieves even niche penetration, it will probably be the end of eSATA — always an awkward bus, technically superior but fatally narrow in function, unsupported by most laptops and often only half-implemented on the desktop. Come, USB 3, come, and put this unhappy also-ran out of its misery.

The bottom line

USB 3 marries everything that’s good about USB to performance that’s better than eSATA in most scenarios. To that extent, I am hopelessly in love with it.

But an interface is only as useful as the things it connects, and right now a quick Google search reveals precisely zero USB 3 devices on general sale.

So we’ll have to wait a little longer to see what sort of USB 3 devices appear, and how much they cost, and how quickly consumers take the nascent technology to their bosom. My suspicion, though, is that this upgrade could catch on very quickly indeed.