Question about USB 2.0 and 3.0 cables

[hummer7]

I have several USB 2.0 and USB 3.0 portables wihich came with USB 2.0 and USB 3.0 cables respectively.
One of my recent computer tower has both USB 2.0 and USB 3.0 ports.
I understand that USB 3.0 and 2.0 cables are compatible with either USB 2 or USB 3 ports.

My question is about the speed of file transfer and other functions when USB 2.0 cable (with portable drive with USB 2.0 port) is plugged into USB 3.0 ports in the tower , and vice versa (USB3.0 cable to USB 2.0 port).

 

[DMHolt57]

The cables are not any different, a wire is a wire, connectors are same.

 

[whs]

A USB2 device will always run at USB2 speeds - even when attached to a USB3 port.

 

[hummer7]

OK. If USB 3.0 devices are connected to USB 2.0 port, how speed goes?

 

[whs]

USB 3.0 - Wikipedia, the free encyclopedia

 

[Lady Fitzgerald]

OK. If USB 3.0 devices are connected to USB 2.0 port, how speed goes?

Any device will run no faster than it is designed to be and no faster than the port it is plugged into. In your example, the USB 3.0 device will run no faster than the USB 2.0 port does.

Something to keep in mind about USB speed standards that they are a range. For example, USB 3.0 is basically any speed that is faster than USB 2.0 up to 5.0 Gbps. An inexpensive USB 3.0 device may not run much faster than a high priced USB 2.0 devices.

Also keep in mind that not all USB ports will run at maximum speed for the standard nor be able to provide the maximum amount of power for the standard.

 

[pbcopter]

The cables are not any different, a wire is a wire, connectors are same.

The cables are different in that USB 3.0 has more wires and thus more pins on the connector.

They are arranged to provide compatibility with USB 2.0

See the link that whs provided.

 

[alphanumeric]

The USB 3.0 cables that came with my external drive enclosures don't look like any USB 2 cable I've ever seen. Not the end that plugs into the device anyway. The other end that plugs into the PC looks the same but has extra pins in it.

Keep in mind that even though a device advertises as being USB 3.0 compatible, that doesn't mean it will run at full USB 3.0 speed. My USB 3.0 drive enclosures have 5400 RPM laptop drives in them. They won't even reach full USB 2.0 speeds. I'd have to put an SSD in them to even come close to USB 3.0 speeds.

 

[whs]

Plus there is another problem. The USB3 controllers seem to 'eat' a lot of the 5Mbps. In a series of tests I made, the eSata port was faster than the USB3 port using the same devices - the eSata port is rated at only 3Mbps.

http://www.sevenforums.com/performa...rformance-comparison-hdd-ssd.html#post2631342

 

[LMiller7]

The USB port, cable, end device, plus any intermediate USB devices such as a hub, effectively form a chain. And as is well known the strength of a chain is determined by that of the weakest link. The same principle applies to many aspects of computer performance. If any of the links in the chain are designed only for USB 2, that is the weakest link and will determine transfer speed. The performance characteristics of the stronger links in the chain don't matter. If any device is substandard in quality or operating under adverse conditions it may further reduce performance.

To obtain full USB 3 performance everything in the chain must be of good quality and designed for USB 3.

 

[whs]

To obtain full USB 3 performance everything in the chain must be of good quality and designed for USB 3.

My tests were done on an expensive Dell XPS desktop where one would assume that the setup is optimal. But as you can see from the measurement results, eSata is faster than USB3. The enclosures I used are both from Rosewill.

 

[hummer7]

Thanks to all.
All what you said makes a lot sense.
Have a wonderful new year.

 

[Lady Fitzgerald]

e-SATA is rated for up to 6Gbps; USB 3.0 is only up to 5Gbps. Keep in mind those are only maximum figures and machines could have slower speeds. PCI-e x1 is only 5 Gbps so a card with, say, four SATA 3.0 ports but runs off of only one PCI-e lane hasn't a prayer for full speed if more than one USB 3.0 port is in use at the same time. Yet USB 3.0 cards that run on more than one PCI-e lane are rare as honest politicians.

 

[hummer7]

I have a related question. The USB cables which came with portable drives (USB3) are quite short. (18 inches). I ordered a few 6ft USB 3.0 extension cables to connect with the short USB 3.0. I wonder the use of extension cable would degrade the speed or not.

 

[Lady Fitzgerald]

Possibly, if the cables are poor quality. Generally, six feet add to 18" should not be a problem.

 

[Iain]

I have a related question. The USB cables which came with portable drives (USB3) are quite short. (18 inches). I ordered a few 6ft USB 3.0 extension cables to connect with the short USB 3.0. I wonder the use of extension cable would degrade the speed or not.

Don't forget that there's an order of magnitude difference in bandwidth between USB 2.0 and USB 3.0. The reason USB 3.0 cables are shorter and thicker than the former, is for additional screening and to preserve that bandwidth during transfer of data between two external devices.

I would return those longer cables and move external devices closer to source port.

 

[whs]

I have a related question. The USB cables which came with portable drives (USB3) are quite short. (18 inches). I ordered a few 6ft USB 3.0 extension cables to connect with the short USB 3.0. I wonder the use of extension cable would degrade the speed or not.

Don't forget that there's an order of magnitude difference in bandwidth between USB 2.0 and USB 3.0. The reason USB 3.0 cables are shorter and thicker than the former, is for additional screening and to preserve that bandwidth during transfer of data between two external devices.

I would return those longer cables and move external devices closer to source port.

 

[LMiller7]

For USB 2 the maximum cable length is about 16 feet. USB 3 doesn't specify a length limit but no more than 10 feet (3 meters) is recommended. But cable quality is more important then length. A cheap cable 6 feet long could limit speed.

See this for more information:
USB Cable Length Limitations And How To Break Them