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HOW IS USB 3.0 BACKWARDS-COMPATIBLE WITH USB 2.0 ?

Shenzhen STC Cable Manufacturer | Updated: Mar 10, 2016
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Since USB has proven itself to be the overwhelming favorite interface, a crucial pillar of the USB 3.0 specification addresses how the SuperSpeed interface must remain compatible with the millions of existing USB computers and devices in the marketplace. For the most part, it's good news: all USB 2.0 devices will work on USB 3.0 hardware, and (nearly) all USB 3.0 devices will work on USB 2.0 hardware.


As part of the requirement, all USB 3.0 ports include the necessary pins and logic to process USB 2.0 signals, and all of the receptacles are physically compatible with their earlier counterparts. This means that computers and infrastructure can be upgraded to USB 3.0 at any time, ensuring future-compatibility without compromising on existing functionality.


Similarly, all USB 2.0 ports will be compatible with USB 3.0 signals, as all SuperSpeed devices are required to be capable of interfacing on their 2.0 pins alone. This means that a USB 3.0 hard drive (for example) can attach to a USB 2.0 computer using a 2.0 cable, or attach to a USB 3.0 computer using a 2.0 cable, or attach to a USB 2.0 computer using a 3.0 cable. While the device will not benefit from the higher bandwidth of the USB 3.0 interface, it is still required to function properly at full USB 2.0 speeds.


THE EXCEPTION: The one catch to backwards compatibility is that the SuperSpeed USB B male connector is not able to interface with a USB 2.0 B female jack. This situation will only occur with a device featuring a built-in (non-removable) USB Powered B connector, and is intentional because a USB 2.0 port is not capable of powering a USB 3.0 Powered B device. In any other situation involving USB 3.0 B and USB 2.0, there is compatibility either at the USB A end of the connection, or by using a USB 2.0 cable.


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