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USB 3.0: What You Need To Know
It's fast. The new standard breaks the 480Mb/s data transfer limit of USB 2.0 and takes it to a new theoretical maximum of 4.8Gb/s. Keep in mind that real-world performance can be considerably lower than that. USB 3.0 devices are not expected to reach their full potential at launch, but as the standard matures the USB-IF considers it reasonable to achieve a throughput of 3.2Gb/s, or just about enough to transfer a 27GB high definition movie in little over a minute rather than 15 or more with USB 2.0.
It's bi-directional. Unlike previous versions where data can only be piped in one direction at a time, USB 3.0 can read and write data simultaneously. This is achieved by adding two new lanes dedicated to transmit SuperSpeed data and another pair for receiving it, bringing the total number of connections from four on USB 2.0 (power, ground and two for sending/receiving non-SuperSpeed data) to nine counting the 3.0 ground contact.
Furthermore, the signaling method, while still host-directed, abandons device polling in favor of a new interrupt-driven protocol. This ensures that the USB host controller doesn't continually access a connected device in anticipation of a data transfer. Instead, USB 3.0 devices will send the host a signal to begin a data transfer.
It's more power efficient. The signaling method mentioned directly above also means that non-active or idle devices won't have their power drained by the host controller as it looks for active data traffic. Minimum device operating voltage is dropped from 4.4 V to 4 V. On the other hand, the USB-IF has upped the maximum bus power output from about 500 mA to 900 mA, which will enable power-hungrier devices to be bus-powered and USB hubs to support more peripherals. There's also the bonus that battery-powered devices should charge faster.
It's backwards compatible. Your existing USB 2.0 gear will work on version 3.0 ports and vice versa. You'll be able to maximize your bandwidth when using a USB 3.0 cable with USB 3.0 devices and ports, otherwise plugging a 3.0 device into a 2.0 port or a 2.0 device into 3.0 a port will get you standard USB 2.0 data rates.
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It's bi-directional. Unlike previous versions where data can only be piped in one direction at a time, USB 3.0 can read and write data simultaneously. This is achieved by adding two new lanes dedicated to transmit SuperSpeed data and another pair for receiving it, bringing the total number of connections from four on USB 2.0 (power, ground and two for sending/receiving non-SuperSpeed data) to nine counting the 3.0 ground contact.
Furthermore, the signaling method, while still host-directed, abandons device polling in favor of a new interrupt-driven protocol. This ensures that the USB host controller doesn't continually access a connected device in anticipation of a data transfer. Instead, USB 3.0 devices will send the host a signal to begin a data transfer.
It's more power efficient. The signaling method mentioned directly above also means that non-active or idle devices won't have their power drained by the host controller as it looks for active data traffic. Minimum device operating voltage is dropped from 4.4 V to 4 V. On the other hand, the USB-IF has upped the maximum bus power output from about 500 mA to 900 mA, which will enable power-hungrier devices to be bus-powered and USB hubs to support more peripherals. There's also the bonus that battery-powered devices should charge faster.
It's backwards compatible. Your existing USB 2.0 gear will work on version 3.0 ports and vice versa. You'll be able to maximize your bandwidth when using a USB 3.0 cable with USB 3.0 devices and ports, otherwise plugging a 3.0 device into a 2.0 port or a 2.0 device into 3.0 a port will get you standard USB 2.0 data rates.
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