Thursday, January 14, 2010

USB 3.0 Offers Gbps Data Transfers

USB nearly fulfilled the promise of its name to be the universal serial bus when USB 2.0 replaced 1.1 as the computer standard. The introduction of USB 3.0, also called “SuperSpeed”, looks to increase that domination with a 10x speed increase.

USB 2.0 Cable soon to be replaced by USB 3.0What’s wrong with the current 480 Mbps USB speed? Nothing at all for many peripheral devices. It sure beat the 1.5 to 12 Mbps capability of the original USB 1.0 and made USB practical for things like video transfers from camcorders. Most video cameras now have a mini-USB connector in place of the FireWire interface that was thought to be the high speed option.

But look at what you get with USB 3.0. The speed goes up by a factor of 10x to 4.8 Gbps. In practice, you can expect to get around 3.2 Gbps or 400 MB per second through a 3.0 interface. That’s the transfer mode they are calling SuperSpeed. If you have a computer and a video camera that both sport USB 3.0 interfaces and a cable rated for the new spec, you can enjoy that truly super speed transfer mode. But like the USB 2.0 upgrade before it, USB 3.0 is compatible with the earlier USB interfaces. You can even use your old cables and they’ll work just fine.

So what’s the magic behind SuperSpeed and why do you need a different cable? In order to get that screaming performance that can approach 5 Gbps, USB 3.0 adds additional signal wires. USB 3.0 cables have the same power and ground wires, the same 2 wires for non-SuperSpeed data, and 4 more wires for SuperSpeed. Those four wires are configured as two differential pairs, allowing USB to upgrade from half-duplex to full duplex operation. That means communications in both directions at the same time. The connectors on the cables and receptacles change so that USB 2.0 cables won’t connect with the extra SuperSpeed connections.

The signaling protocol itself has also been enhanced so that SuperSpeed can establish a direct connection or communications “pipe” between host and peripheral instead of broadcasting all data to all devices on the bus. Bulk transfer is improved by allowing multiple streams of data through a single bulk pipe.

You know that USB has become a power bus as well as a data bus for many small devices. You expect to be able to charge your iPod or MP3 player while you are uploading new songs. There are even gadgets like personal fans or gooseneck LED lamps that have no data function. They just use the power provided by an open USB port. Most ridiculous is the USB coffee warmer or blanket. Well, USB 3.0 won’t put an end to any of that. In fact, the bus power available has been increased from 100 mA to 150 mA for unconfigured devices and from 500 mA to 900 mA for configured devices. Now higher power devices can get by without the inconvenience of an extra wall wart power supply.

USB 3.0 is just starting deployment, so don’t expect every device you see on the shelf to be sporting this interface. However, you can bet that PC makers will be taking note and adding this capability as a way of distinguishing their products, just like Blu-ray drives have moved into high end products. External drive manufacturers and camcorder companies also have a lot to gain from the higher transfer speeds of USB 3.0. If video is the killer app, then USB 3.0 is going to be a major enabler.

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