Low-Power USB Ports Haunt My MacBook Pro

It turns out that Apple made at least a few errors in designing the hardware of the MacBook Pro.  After living with it for a solid week, I can report that, along with the useless ambient light sensor and wimpy power cord, both of the ‘Pro’s USB ports are compromised!  The left side doesn’t have the power to spin up a disk drive, and the right side shares bandwidth with the iSight camera built into the lid.  Why would Apple make this kind of mistake when PC vendors get these things right?

My initial disappointment that the 15″ MacBook Pro has just two USB ports, one on each side, was tempered by the fact that lots of other notebooks have the same problem.  Where my old Dell XPS M1210 had two ports on each side, my new XPS M1330 has just one per side. On the other hand, the Mac does feature a pair of FireWire ports, one 400 and the other 800 and both using full-size connectors, while the Dells each have just a single mini 400.

But, as many have discovered, not all USB ports are created equal.  There are three things to consider when it comes to USB ports:

1. Low-speed, full-speed, and high-speed – Most folks know that the old slow USB standard was updated with something often called USB 2.0.  But, given that nearly all controllers support both the old and new standards these days, this consideration is largely irrelevant.  One thing that may surprise you is that modern controllers support “virtual” USB ports for each speed – connect a low-speed device in a high-speed port, and it is connected to a different bus than would be used by a high-speed device connected to the same port.
2. Hidden hubs – Most people don’t realize that most devices have internal USB hubs hidden inside, sharing bandwidth between connected peripherals and internal system components. In practice, this means that a device’s speed can vary depending on which physical port you plug it into.
3. Power – Not all ports are supplied with the same amount of electrical current, either.  If a peripheral uses a lot of power, it can fail to work in one port and work fine in another.  Disk drives are especially hungry, so many vendors supply them with “Y cables” that plug into two ports at once.  This is a big problem for add-on cards, too, since most PCMCIA / CardBus / ExpressCard slots don’t supply much power at all.

I haven’t had much trouble with this in the past, but these issues reared their heads with my new MacBook Pro.  It seems that both of the Mac’s USB ports are limited:

1. The left-hand port (by the MagSafe connector) does not offer enough power to spin up my Maxtor OneTouch Mini 4 hard drive. This is a shame, since this high-speed port is not shared with any internal devices and thus should be faster.  Low-speed devices using this port, however, have to share bandwidth with the internal BlueTooth transceiver.
2. The right-hand port offers enough power for every drive I’ve tried, but shares high-speed bandwidth with the built-in iSight camera.  Low-speed devices like my KVM‘s keyboard and mouse cable share a hub with the internal keyboard and mouse.

Although neither port is really perfect, it seems that I will tend to use the right-hand port more when I am traveling since I won’t have to worry about power.  Because I’ve already found myself juggling connectors, I’ll probably end up attaching a powered hub to the left port to use when I’m at home.

None of this is really critical – the system works fine.  But I’m somewhat disappointed that Apple would design in a frustration like this.  How many non-technical folks are going to buy a USB drive and assume it’s flaky because it doesn’t work half the time?  And how many will visit the genius bar when they notice the pattern of left-side/right-side?  The MacBook has the same power issue, too.  For the record, my Dells work fine…