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What is a USB Cable?

USB jack.
USB cable.
A variety of USB cables, including micro-USB, mini-USB, and standard USB.
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  • Written By: Brad Cole
  • Edited By: Lindsay D.
  • Last Modified Date: 16 March 2014
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A Universal Serial Bus (USB) Cable is primarily used to connect a USB device to a host. Common hosts include computers and video game consoles. While there are multiple USB standards, cables that are fully compliant with USB 1.1 specifications will work with USB 2.0 technology and vice versa. USB cables can be identified by the USB trident on top of the plug overmolds of type “A” and “B” connectors.

A USB cable can have numerous types of plug ends, the style of which is called a connector. Connector types include Standard-A, Standard-B, Mini-B, Micro-A, Micro-B, and Micro-AB. These plugs go into corresponding receptacles built into hosts and devices. Standard-A receptacles are the type commonly referred to as USB ports on computers; Standard-B receptacles are usually found on large peripheral devices such as printers and scanners; Mini and micro receptacles are usually on small devices like digital cameras and cellular phones; Mini-AB receptacle are, according to the standard, only on USB On-The-Go devices. Most USB cables that connect a device to a computer will have a Standard-A plug on one end and another type of plug on the other.

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Beyond connector types, compliant USB cables are not proprietary. A standard cable can connect a device to a Macintosh or a Windows PC, for example. The software within the device, however, may not work with the host. In addition, some companies create cables that appear similar to USB cables but are not compliant with USB standards — such connectors should not have the trident logo on them.

A standard USB cable contains multiple wires. One wire contains a path for a five volt (5V±5%) power supply; two are twisted-pair data wires; and one is a ground.

A USB cable under 2.0 specs can only be five meters (roughly 16.4 feet) long. This limit was established due to a cable delay spec of 26 nanoseconds, which allows for reflections to settle at the transmitter before the next bit is sent. USB hosts must have their commands answered within an allowed time frame or they will consider the commands lost — cables significantly longer than five meters would result in too much of a delay.

There are many solutions for connecting USB devices beyond the 5 meter cable limit. These solutions include using extender cables, which are self-powered hubs with a fixed 10 meter cable and a one-port bus powered hub in the middle; using up to five hubs in a chain; and building a bridge that acts as a USB device on one side and has a host controller at the other end. It's best to use a long-haul signaling protocol like Ethernet or RS-485 in the middle if this method is used.

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Discuss this Article

honeybees
Post 6

I don't use nearly as many USB cables as I used to. Now most of my devices are wireless and this is so much better than having cables all over the place. When I bought my current PC several years ago I was so excited because it had 5 places where you could plug in a USB cable. Now I find that I rarely use my PC and also hardly ever need a USB cable anymore.

SarahSon
Post 5

I had to start labeling my digital camera USB cables because I had about three of them at one time. I had several different digital cameras and they all used a different USB cable. They all looked very similar, but they were all different and you had to have the right one in order to download the pictures from the camera to the computer.

Before I labeled them I would guess which USB cable was the right one, and it was always the last one I choose.

pastanaga
Post 4

@Fa5t3r - Unfortunately, I don't think that's going to happen anytime soon. Even among USB cables there are different sizes at the moment. You can get connectors for them, but those can be pricey as well.

Basically, the best thing to do is make sure that you get quality cables that are in a good position on the machine so that you aren't going to be constantly nudging them in order to keep them from wearing out. This applies to USB and every other kind of cable.

Fa5t3r
Post 3

@gremlins - I love the fact that so many things can be connected with the same wires. It really annoys me when I buy something and the wire wears out after a few months, but it costs about $50 or even more to get a new connection. I really think some of the companies do this deliberately, they make sure that the wires aren't compatible with anything else so that you are forced to pay out for a new one.

If everything was made into a standard USB data cable it wouldn't be soon enough for me.

watson42
Post 2

I remember when USB cables were "new". Crazy how quickly they became a go-to way to connect different types of computer equipment and other gadgets, from cameras to cell phones.

gremlins
Post 1

It's amazing to me how many devices use USB cables, whether they're standard, mini, or micro USB cables. A lot of the peripherals on my computer have USB cable connections, such as my printer and the foot pedal I use for the general transcription I do occasionally. In addition, I've had phones that have used mini USB cables to connect to my computer to transfer pictures and music, and my current phone uses a micro USB cable. With the growing popularity of USB devices, it's no surprise that so many different types of hubs exist to connect them.

What about you guys, are you drowning in USB cables too?

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