How-tos

Why Do USB Connections Need Three Tries?


USB meme
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It’s happened to everyone: You try to plug in a USB connector, and it doesn’t work. So you flip it, and it still doesn’t work. Frustrated, you flip it a third time—and it fits! Why is this experience so common with USB?

Decades of Flipping USB Cables Around

We’re talking about the classic USB hardware here—specifically, the “type-A” connector that dates back to USB’s first release in 1996.

Modern USB-C connectors don’t have this problem. You can plug them in either way. USB has definitely improved on its design, and the problem is going away.

But we’ve still been flipping those USB sticks back and forth for decades now. So let’s look at why that is.

RELATED: 25 Years of Making Connections With USB (After Three Attempts)

The Joke Explanation: USB Superposition

Many geeks have speculated that USB connections have a sort of “superposition.” You must spin a USB device around three times because it has three states—up, down, and a third position we do not fully understand. Only in this position will the connection be in a correct, pluggable state.

That’s all pretty funny, but of course, it’s just a joke. However, it’s funny because there does seem to be something unusual about USB compared to the other common connectors we use every day.

These USB connection issues are a meme at this point. This problem is also known as the “USB paradox”: If there are only two ways a USB connector can fit, why does it take three tries to plug it in?

A Design That Appears Symmetrical but Isn’t

The inside of a USB port and connector.
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Physically, a USB type-A connector appears to be symmetrical. It’s rectangular in shape. Unlike HDMI, for example, there’s nothing about the physical shape of the connector that makes it look like one side is up and one side is down.

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But it is! Just look inside the connector and you’ll see that it isn’t symmetrical. One side must be up and one side must be down.

But unlike with something like HDMI, there’s nothing about the shape that makes it easy to tell which side is up and which side is down. USB is just asking for trouble.

It’s Unclear Which Side Is the Top

Without any clear indication of which side is actually the top of the USB cable, you don’t have much choice. You either carefully look at the inside of the connector, or you flip it around and experiment, right?

Actually, the USB standard tries to help.

Did you know that there is something that’s supposed to tell you which side is the top of the USB connector? There’s often a USB logo on top of the connector, and you can see it—and possibly feel it with your fingers. If you see the logo while looking down at the USB connector, then you know that the USB connector is in its correct orientation and that you should just be able to plug it in.

If you have a vertical USB connection—for example, on the back of your monitor—the USB cable should be plugged in with the logo on the connector facing you.

The USB logo on top of a USB connector.
Jin Odin/Shutterstock.com.

This logo position is required by the official USB specification, but not every company follows it. Since not every USB connector has a logo on it, you can’t take this for granted. Also, on some devices, the USB ports themselves are upside down inside the device—this may be necessary to fit a bunch of components inside a laptop, for example.

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So, not only do most people not know about this logo trick, but it also doesn’t necessarily work all the time.

Even if you know the trick, you might still find yourself flipping the connector three times, just trying to find which orientation is correct by trial and error.

Trial and Error—but Why Three Times?

So, with a connector with an unclear design and unreliable marking of which side belongs on top, what do you do?

Sure, you could look at the inside of the USB connector and the inside of the USB port you’re plugging it into and determine the correct orientation with your eyes. But why bother? It may be difficult to see the inside of the USB port—for example, if it’s on the back of a computer. It also may be dark in your room. You just need to try two orientations and see which one works—in theory.

To save time, people just try inserting a USB device and seeing whether it works. Did it not connect? Flip it around, now it will work—well, not always. Sometimes you have to flip it again.

Again, it all comes down to USB Type-A’s design. When you’re trying to connect a USB device, it’s very easy to bump the edge of the connector against the edge of the USB port—or the metal or plastic next to it. This feels about the same as if you have the USB connector upside down.

You probably don’t want to apply any extra force or jiggle it around—because why force it? You may have the device upside down. Just flip it and try the other way. But if even that doesn’t work, you know for sure that you’re doing something wrong. You have to apply some extra force and push harder, or you have to jiggle the connection around to correctly align it, or you have to feel the port with your finger to ensure that it’s correctly aligned.

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In other words: Even when you’re kind of close, a USB Type-A port doesn’t necessarily guide your connector in. There’s no clear, tactile feedback that you’re just missing the connection in the correct orientation. It feels the same as if you have the connector the wrong way around.

When you think about how people often start inserting a USB device, the first attempt is kind of a “test”—does it go in easily? If not, you might have the device the wrong way around. Flip it and try again. If even that doesn’t work, you’ll need to flip it back to the first position and try a little harder.

It’s Not You, It’s USB

Ultimately, the problem isn’t with you—it’s with the USB Type-A connector. It’s just designed in an unclear way that leads to this problem. Why it’s designed that way is a question only the designers can answer.

The good news is that we’ve learned from the history of flipping USB sticks and other devices around three times. USB Type-C is reversible, so you’ll never have to flip it—just plug it in either way. The USB4 standard requires USB Type-C, so USB Type-A is slowly and gradually being phased out.

One day, future generations won’t even understand the USB-flipping meme.

A USB4 cable with a Type-C connector.
Alexander_Evgenyevich/Shutterstock.com

RELATED: USB Type-C Explained: What is USB-C and Why You’ll Want it





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