Not all USB ports are created equal

Ever plugged an external USB hard drive directly into your computer, only to find it doesn’t properly start up?

Perhaps you’ve found upon plugging in, that your iPhone resides in a phantom world: it does not charge or is not recognised at all.

Or maybe you’ve just found yourself thinking “my god, these files should not be transferring this damn slowly…”

If you answered yes, then rest assured that you’re not just a crazy, power-hungry speed demon. I am here to confirm what you and I have suspected all along: The desktop PCs, MacBook Pros, PC laptops and even iMacs you place so much faith (and hard-earned dollars) in, are continually released with sub-powered USB ports, all the time. Who pays for the inconvenience? We do.

Many times I have hooked up let’s say, a 4-port USB hub, only to plug in a device and not have it show up. This happened whether the hub was powered or not, and even if the port had no other devices plugged in.

Here is why:

The rear-USB port of MacBooks is actually part of an internal USB hub, shared with the keyboard, bluetooth, IR receiver and iSight camera. This leaves very little power for the USB port itself. Shithouse hardware design, Apple.

The rear USB port, the one nearest the screen, is in fact already on an internal hub, shared with everything USB inside the case: the keyboard, the Bluetooth, the trackpad, the iSight camera and the infra-red receiver. Adding any device to this is bound to end in disaster, even a powered USB hub.

This may sound like a problem that only technical nerds should care about. However, the average computer user should care. For starters, USB is still very much the standard by which billions of devices are powered. The USB 2.0 standard is itself insanely relied upon to meet it’s own specifications: Namely, that it is 40 times faster than USB 1.0.

To compare:

  • USB 1.0 ports should have enough power to transfer data at 12Mbps.
  • USB 2.0 ports should have enough power to transfer data at 480Mbps.

Accounting for bottlenecking of the hardware in use, and other impurities, the USB port may not reach these ideals but it should still deliver sufficient power and speed to be able to operate effectively pain-free.

The sad reality is, even adjacent USB ports built into high-end machines deliver ridiculously different performance capabilities, and this seems to be due to poor or lazy hardware design.

Refer to the below graphs which compare a 2010 Core i7 MacBook Pro’s two USB ports data performance. You would think that “the BMW of laptops” would have their two (hardly even generous) USB ports operating at close to ideal / equal speeds. Think again.

Speed/power comparison of two USB ports built into the i5/i7 Macbook Pro

Speed/power comparison of two USB ports built into the i5/i7 Macbook Pro

These sorts of results might reveal why manufacturers often shy away from adding more than a couple of USB ports to their laptops. Getting adequate power to them obviously poses a problem. At this stage, we have no solid explanation as to why, however theories hold for portable notebooks / laptops that this may be a somewhat deliberate capping in an effort to preserve battery life.

Despite this, the future looks bright for the standard, with Wireless USB for data and a low-power, 10x higher data transfer speed USB 3.0 standard both gaining adoption in the market. The mention of “low-power efficiency” troubles me, given the above issues deriving from lack of enough power to drive the 3rd-party device connected.


Source: DJ TechTools    MacBook USB Port Inequality.

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Categories: Science, Technology

Author:Andrew Beato

CEO, Chief Editor and founder of Intentious. Passionate comment enthusiast, amateur philosopher, Quora contributor, audiobook and general knowledge addict.

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4 Comments on “Not all USB ports are created equal”

  1. Nic
    May 17, 2011 at 9:30 pm #

    There are a few errors in this post. For example it is suggested that a lack of power results in slow speed. This is not the case. Newer macs (and some other brands too) can deliver well in excess of the standard 500ma per port. The newer MacBook pros can output 1600ma to charge high current devices such as iPads.

    In relation to the problems, I get these problems on my Dell and my MacBook. My understanding is that the Intel chipset isn’t all that great, for example, the chipset in my dell (ICH9) only has two high speed controllers for 4 USB ports, internal USB devices and USB ports on the dock! You can find these details on the Intel website or by looking in device manager for USB2 or EHCI controllers.

    I am not a hardware engineer but I imagine the designers added the hub in order to manage the lack of high speed USB controllers (If any hardware engineers know for sure please share!) USB has a high overhead and it also suffers badly when other devices try to share the bandwidth and hubs introduce delays, all these things reduce performance.

    I would love to see Apple use a discrete pcie chipset, It would open the door to USB3 and improve performance. In reality I imagine it would be difficult to fit more hardware in the already cramped cases for not a lot of benefit.

    • May 19, 2011 at 3:01 pm #

      Good points Nic. Very interesting that the limitation lies with Intel.

      I guess my beef iwith makers like Dell and Apple are that regardless of the reason, they deliberately choose not to acknowledge that only one is adequately powered. It seems like a mini con. Although some tech-savvy may be aware of it, the average consumer is not, nor will they be. As far as I’m concerned, if I’m paying a premium for better designed hardware, I expect the makers to find a way to adequately power all the USB ports they include… or at least colour/label it if not, like someone else mentioned.

      It’s ridiculous that although I have a port free on my Macbook Pro 2011, and paid $1000 more for a “premium machine”, I still am forced to use a USB hub to power more than one external hard drive/iOS device.

      Let’s hope with USB3 adoption continuing, and your suggestion of a pcie chipset, this problem is alleviated.

      • eJason
        May 2, 2013 at 2:46 pm #

        Yeah, you said it., Andrew. I too am not so much concerned with the bare fact that a port is sharing power, and there are external hubs after all. What makes me actually annoyed is that this is only known through the grapevine as gossip, people like you being the ones to spread this essential information to those who are wondering why their USB port seems to be defective (and thank you).

        I’m sick and tired of far too many major manufacturers putting out a product, and even when there has been a lot of work put into design, marketing, quality, they seem to forget that a very crucial factor of a successful, high quality, respectable product, is none other than *documentation*. I would say that a product is in fact only as good as its documentation, and in fact, as a student of software engineering, my classmates/teammates and I absolutely spend far more time working on solid documentation, than we ever spend on implementation. Only when planning is added to the development time does documentation become less than half of the overall time and effort spent.

        Personally, I find far too much “documentation” these days to be more of a sales pitch ridiculously aimed at those who have already made the purchase, with a heap of self-congratulation for a list of features, with the less obvious but still important details of those features being lost somewhere in the excess glitter and showmanship…

  2. eJason
    May 2, 2013 at 2:30 pm #

    I have the “Late 2011″ MacBook Pro 17”, and I have definitely experienced this. I have known about this for quite some time now, but had to look this up to remember which one it was, since I have not for a while had power throughput problems.

    The reason that I haven’t had problems and forgot which port was the “runt” is because I have since only used it for my low-profile wireless mouse receiver which takes very little power (so little that if a USB port ever cannot power it, then something is definitely very wrong with the port, as in “broken”).

    And that’s what I’d recommend to anyone that has been burdened by this *blunder* of Apple.

    I can’t imagine that it would have been a terrible design issue at all to simply place an additional USB hub on the motherboard for this port. It strikes me as sheer incompetence and/or lack of concern for quality, than any kind of cost vs practicality issue. Trust me, I paid enough for this laptop that I would hardly blink at the cost of a few extra circuits…

    I would say that, *assuming* there is a good reason for this design, then why not DIVULGE this to we consumers?? Why not just make a note of it in the documentation that I should favor the other ports? That would seem simple enough. Just a little honesty instead of this “you don’t need to know what’s inside the magic black box” nonsense even when we DO need to know!! Not only are our “SOLID GOLD” laptops missing a bit of gold in the center, but we’re not even told that it’s missing. 😉

    Lastly, my heart truly goes out to all of you with only TWO USB ports, one of them more of a half-ass gesture than a feature. I have enough frustration with two useful ports, let alone only one… :-/

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