DifferenceBetween USB 2.0 and USB 3.0

What is the difference between USB 2.0 and USB 3.0

Submitted by Koder on Thu, 01/07/2010 - 13:48 

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There is a new standard in the USB world called USB 3.0, in this article we will discuss the difference between USB 2,0 and USB 3.0. Universal Serial Bus or USB, as you all know is the most popular connection standard between devices and a host controller (usually located on a computer). USB has undergone many revisions and the latest USB hardware spec to come out is version 3.0, after version 1 and 2. Everything from your flash drives, mice, keyboard, PDAs, Game Consoles, GPS chargers, cell phone connectors and chargers,  GPS devices and bluetooth head sets all use USB in one form or the other. So lets see whats the differences between the most popular USB 2 and just out USB 3 standard are

USB 3.0 Highlights and Benefits over USB 2.0

• Transfer rates - USB 2.0 offers transfer rates of 480 Mbps and USB 3.0 offers transfer rates of 4.8 Gbps - that's 10 times faster.
• Addition of another phsyical bus - The amount of wires has been doubled, from 4 to 8. Additional wires require more space in both the cables and connectors, so there are new types of connectors.
• Power consumption - USB 2.0 provides up to 500 mA whereas USB 3.0 provides up to 900 mA. The USB 3 devices will provide more power when needed and conserve power when the device is connected but idling.
• More bandwidth - instead of one-way communication, USB 3.0 uses two unidirectional data paths, one to receive data and the other to transmit while USB 2.0 can only handle only one direction of data at any time.
• Improved bus utilization - a new feature has been added (using packets NRDY and ERDY) to let a device asynchronously notify the host of its readiness.

When data is being transferred through USB 3.0 Devices, cables and connectors 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 then 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.

EDITPhysical Differences

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.

Various types of USB Connectors (click to enlarge). From Left to Right: Micro USB Type AB, Micro USB Type B, USB 2.0 Type A, USB 2.0 Type B, USB 3.0 Type A, USB 3.0 Type B, USB 3.0 Type Micro B, Min USB Type A connector

EDITBackward Compatible

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.

Here is a good informational video explaining the various features of USB 3.0 vs USB 2.0

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