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For example on one machine the ports have the empty side on the left and on another it's on the right. Why don't manufacturers make this consistent?

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In addition, why do they always put them so close that half of them is unusuable? – Rook Dec 6 '11 at 18:14
To perpetuate the rule that any USB plug will not go in first time, nor will it go in when rotated through 180, it will, however, go in with no problems when turned back round to how it was the first time you tried it. – Tog Dec 6 '11 at 19:11
+1 my OCD friend! Most people don't notice this. – Moab Dec 6 '11 at 19:18
I've been wondering the same thing with the direction of the text on the spines of books. That bothers me a lot more to be honest. – Daniel Beck Dec 6 '11 at 19:45
@Tog: from – BlueRaja - Danny Pflughoeft Dec 6 '11 at 22:18

There are two simple reasons. First, there is no defined community standard. Each manufacturer makes their devices however they see fit. So, ports are put wherever they desire.

The second reason is because designers of devices, especially small ones, must first lay out their circuit boards and other internal components so that they can squeeze as much hardware into the smallest amount of space. Ports are a major part of that process, but there is also a bit of aesthetic trad-off when it comes to laying out all the hardware in the smallest footprint possible while also remaining functional.

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+1: If it isn't defined, by definition is is undefined and any behavior is ok. – surfasb Dec 7 '11 at 1:48

Most USB receptacles are mounted to a circuit board, and in general, the "empty" space in the connector is on the side towards the board. This seems to be the de-facto standard construction (if not an actual standard) of PC-board-mount USB connectors, just like D-SUB connectors always have the narrow edge toward the board, and dual PS2 connectors always have the keyboard connector towards the board. (Hint: this is useful to know when blindly connecting cords behind a desk.)

When a USB cord is plugged in, the USB icon will be "on top" of the connector, if the board is toward the bottom. Likewise, the indicator LED on a USB thumb drive will be "on top."

The difficulty is that some manufacturers (*AHEM*Dell*AHEM*) seem to always orient the assembly so the circuit board is above the connector when the PC is in normal orientation. This means that the device plugged into the USB connector will be upside down, so you cannot view the indicator LED.

What I find even more irritating is that USB connectors are allow a limited amount of space for the plug; most thumb drives and many cables are unnecessarily fat so plugging them in blocks other, adjacent USB ports.

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I think it was a standard convention that when plugging a standard USB plug on a horizontal port, the USB logo should be displayed on the upside. This has the side effect that on circuit boards, the empty space would be on the down-side, since most circuit boards are installed such that the majority of the components are on the up side. – Lie Ryan Dec 6 '11 at 22:06

Because there is no need for that... It doesn't matter I guess, since I can't think of a device that may have a problem if attached in either sides. So why would they (manufacturers) do that??

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I bet they would all agree that there should always be one side that is empty. They just wouldn't agree which side that would be.

Setting conventions in a large market full of established players is hard. Perhaps a job for ISO or IEEE.

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I believe the USB symbol on the plug and next to the receptacle are intended to indicate which way the plug has to face to be inserted into the receptacle.

A USB spec says

The USB Icon on the plugs provides tactile feedback making it easy to obtain proper orientation.

However I couldn't find anything about receptacle orientation and, in practice, not all receptacles are marked with the symbol.

Perhaps you would like a flipper plug

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The USB specs do indicate orientation, at least with regard to the how the receptacles are mounted to circuit boards. Look for the receptacle mounting diagrams in the USB Implementers Forum specifications. – Charles Oppermann Jan 7 '15 at 19:57

While there are not standards (as others have said) and there are certainly exceptions to what I shall now claim:

I've found most systems have their USB ports oriented such that when the computer is oriented correctly either upright or horizontally (indicated by the rubber feet usually found on two sides of the computer) and the USB ports are horizontal, the side of the USB device (not the plug in the computer) without the seam (the "empty" side of the device connector) faces up. This would mean the "empty" side of the USB connector inside the computer is normally on the bottom.

Add-in cards may not abide by this, and Apple USB connectors seem to have the connector seams on the opposite side from normal, but for the most part, my observation is that 90% or more of USB devices I've worked with have been oriented this way.

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