USB 3.0 provides better speed and more efficient power management than USB 2.0. USB 3.0 is backward compatible with USB 2.0 devices; however, data transfer speeds are limited to USB 2.0 levels when these devices inter-operate. In 2014, a new standard, USB 3.1, was released and is expected to be in widespread use by 2015.
The newest standard is for USBs is USB 3.1. It offers three major improvements over 3.0: an “always right” C-type connector that plugs in without regard to orientation, higher data transfer speeds of up to 10 Gbps (gigabits per second), and the capacity to power any type of device.
The C-type connector is small enough for modern, slim devices, such as MacBook Air-type notebooks, tablets, and smartphones. but still robust enough for 10,000 cycles of use. Data transfer speeds are more in sync with current app and user needs, especially for video and image files. And the option to connect to and power any type of device, with 100 watts of charging power that can be divided between two devices, greatly reduces “charger and cable clutter,” simplifying connectivity between personal devices. However, backwards compatibility will be limited.
When data is being transferred through USB 3.0 devices, cables, and connectors, the transaction is initiated by the host making a request followed by a response from the device. The device either accepts the request or rejects it. If accepted, the device sends data or accepts data from the host. If there is lack of buffer space or data, it responds with a Not Ready (NRDY) signal to tell the host that it is not able to process the request. When the device is ready then, it will send an Endpoint Ready (ERDY) to the host which will then reschedule the transaction.
USB 3.0 Connectors are different from USB 2.0 Connectors and the 3.0 connectors are usually colored blue on the inside in order to distinguish them from the 2.0 connectors.
USB 3.0 is compatible with USB 2.0. However, the USB 3.0 product will perform at the same level as a USB 2.0 product, so speed and power benefits will not be fully realized.
USB 3.0 receptacles are electrically compatible with USB Standard 2.0 device plugs if they physically match. USB 3.0 type-A plugs and receptacles are completely backward compatible, and USB 3.0 type-B receptacles will accept USB 2.0 and earlier plugs. However, USB 3.0 type-B plugs will not fit into USB 2.0 and earlier receptacles.
This means that USB 3.0 cables cannot be used with USB 2.0 and USB 1.1 peripherals, although USB 2.0 cables can be used with USB 3.0 devices, if at USB 2.0 speeds.
The following videos review the speed of USB 2.0 vs USB 3.0 products:
For a similar product, the USB 3.0 version is generally more expensive than its USB 2.0 version.