do-usb-three-connections-require-usb-three-cables-00

If you are new to the world of USB 3.0, then you may have plenty of questions about the cables you can and/or should use with USB 3.0 enabled devices. With that in mind, today’s SuperUser Q&A post helps a curious reader learn the “ins and outs” of USB 3.0.

Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-driven grouping of Q&A web sites.

Photo courtesy of Xiao Zong Zong (小宗宗 – Flickr).

The Question

SuperUser reader Xavierjazz wants to know if USB 3.0 connections require USB 3.0 cables in order to reach their full speed potential:

Do USB 3.0 connections require USB 3.0 cords to reach USB 3.0 speeds? Will any USB cord support any USB 3.0 device?

Do USB 3.0 connections require USB 3.0 cables in order to reach their full speed potential?

The Answer

SuperUser contributors Steven and fixer1234 have the answer for us. First up, Steven:

A USB 3.0 cable is required for USB 3.0 speeds, but any USB cord will make a connection.

Source 1: USB [Wikipedia]

SuperSpeed (USB 3.0) is supported only by USB 3.0 and newer interfaces, and requires a connector and cable with extra pins and wires, usually distinguishable by the blue inserts in connectors.

Source 2: USB 3.0 Super Speeds [USRobotics]

USB 3.0 cables can be used with 2.0 devices and ports if the connector types fit (no B Male or B Micro connectors), but the transfer rate will fall back to 2.0.

Source 3: Are USB 3.0 cables different? [UserBenchmark]

To get USB 3.0 speeds, you need special USB 3.0 cables. Yes, USB 3.0 cables are different. Even though you can connect a USB 3.0 device via a USB 2.0 cable, in order to achieve full USB 3.0 speeds you need to rewire any existing cabling. USB 3.0 cables have more internal wires, are usually blue, and are noticeably thicker than the old USB 2.0 cables. We figured this out the hard way during the USB flash drive group test.

Followed by the answer from fixer1234:

You cannot achieve USB 3.0 speeds without a USB 3.0 cable. However, speed is not the only issue.

A USB 2.0 cable will work (at USB 2.0 speeds), for some, but not all, USB 3.0 devices. There are at least three important differences in cable construction between the two standards.

Related to Speed:

  • USB 3.0 cables have nine internal conductors versus four in USB 2.0 cables.

Four of the nine internal conductors match the USB 2.0 configuration (two are for power and two are for signal). Connecting a USB 3.0 device with a USB 2.0 cable uses those conductors and operates like a USB 2.0 device.

The other five are signal conductors which are used for the communication method that provides USB 3.0 super speed. A good general description can be found here: USB 3.0 [Wikipedia]

  • USB 3.0 cables have a limit of three meters versus the USB 2.0 limit of five meters.

(Note that this is a practical limit.) The cable can be any length as long as it meets all of the electrical requirements in the specification. The three meter limit is based on maximum allowable losses using the largest recommended wire size so that the cable is flexible. Specs Document [Zip File – USB.org]

Related to Power:

  • A USB 2.0 cable may not be adequate for a high current USB 3.0 device.

Some USB 3.0 devices draw more power than USB 2.0 devices. The power conductors in USB 3.0 cables need to be able to carry 900 mA versus 500 mA for USB 2.0 cables.

Additional information on USB 3.0 versus 2.0 can be found here: USB 2.0 vs. USB 3.0 [Diffen]


Have something to add to the explanation? Sound off in the comments. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion thread here.