Feeds

Inside USB 3.0

What makes SuperSpeed tick

Build a business case: developing custom apps

Since USB 3.0 incorporates USB 2.0, plugging a USB 3.0 printer into a USB 2.0 port on your PC will still work, but without the benefits of the faster bus. The USB 2.0 add-on doesn't even need to know the computer it's connected is a SuperSpeed device, it'll just work as if the PC has USB 2.0. Existing drivers will continue to work.

Bus Architecture

USB 3.0's dual-bus architecture

SuperSpeed USB has a dual-bus architecture to allow hosts to run USB 3.0 right alongside USB 2.0 - hence that USB 2.0 cable tucked inside the USB 3.0 cord. But while hosts and hubs will be able to operate USB 2.0 and USB 3.0 buses simultaneously, plug-in peripherals will not.

So there'll be no combining both buses to get an aggregate bandwidth of 5.4Gb/s.

However, it does mean that a brand spanking new netbook with USB 3.0 ports but running Windows XP as its OS won't lose USB functionality, only the SuperSpeed operation.

Running the USB 3.0 part independently of the USB 2.0 bus is necessary because the new bus uses different protocols, though it retains USB 2.0's data transfer types and pipe model to make it easier for driver writers to make use of existing code. SuperSpeed transmits data in packets, as USB 2.0 does, but this time devices explicitly route packets from the source to the target. Compare that to USB 2.0, which simply broadcasts all packets to all connected devices whatever they may be and whether they're the intended recipient or not.

The new approach has a couple of key advantages. First, it means you'll be able to connect many more devices: up to 127 of them chained in up to five tiers of hubs, each of which can drive up to 15 ports. Secondly, it makes for a far more power-efficient bus.

Packets are sent asynchronously and assembled into files at the end of their journey. Links in the route-chain are used only when they're needed. There's no need for devices to continually poll the link for incoming data.

Send a file to a USB Flash drive, and the packets will move from device to device down the chain according to a direct route encoded into the packets' headers. Each step of the journey is initiated at a signal from the host, which knows where each packet is coming from and where it's going.

USB 3.0 SuperSpeed

Hubs are more like routers in USB 3.0

The host is always part of the chain, so a packet sent from a connected camera to a Flash drive is routed first to the host and then out to the storage gadget.

Build a business case: developing custom apps

More from The Register

next story
iPad? More like iFAD: We reveal why Apple fell into IBM's arms
But never fear fanbois, you're still lapping up iPhones, Macs
Sonos AXES support for Apple's iOS4 and 5
Want to use your iThing? You can't - it's too old
You didn't get the MeMO? Asus Pad 7 Android tab is ... not bad
Really, er, stands out among cheapie 7-inchers
Apple winks at parents: C'mon, get your kid a tweaked Macbook Pro
Cheapest models given new processors, more RAM
4K video on terrestrial TV? Not if the WRC shares frequencies to mobiles
Have your say with Ofcom now, before Freeview becomes Feeview
Leaked Windows Phone 8.1 Update specs tease details of Nokia's next mobes
New screen sizes, dual SIMs, voice over LTE, and more
Microsoft stands on shore as tablet-laden boat sails away
Brit buyers still not falling for Windows' charms
prev story

Whitepapers

Implementing global e-invoicing with guaranteed legal certainty
Explaining the role local tax compliance plays in successful supply chain management and e-business and how leading global brands are addressing this.
Consolidation: The Foundation for IT Business Transformation
In this whitepaper learn how effective consolidation of IT and business resources can enable multiple, meaningful business benefits.
Backing up Big Data
Solving backup challenges and “protect everything from everywhere,” as we move into the era of big data management and the adoption of BYOD.
Boost IT visibility and business value
How building a great service catalog relieves pressure points and demonstrates the value of IT service management.
Why and how to choose the right cloud vendor
The benefits of cloud-based storage in your processes. Eliminate onsite, disk-based backup and archiving in favor of cloud-based data protection.