Our Blog

I discovered something interesting this weekend.

I had a need for a new external USB hard drive and rather than buy my usual Western Digital MyPassport drive I decided to spend a little more and get a Toshiba drive. Why? Instead of being made of plastic it was made of brushed aluminium which I preferred.

When I got home I discovered it needed 2 USB ports to work (Toshiba supply a special USB Y cable for just this purpose) which is less than ideal and poor engineering by Toshiba in my opinion as many other drives work just fine with one USB port.

I thought that this limitation might apply to cheaper laptops that don’t provide enough (ie to spec) power to their USB ports. They should supply 500mA but some can’t manage that. But no, according to the box the Toshiba requires 600mA which is more than the USB specification.

As I didn’t want to use up both of my USB ports I thought I’d cross my fingers and hope that my MacBook Pro would provide enough juice to run the drive from one port. Optimistic I know..
So I plugged the drive into the left hand USB port and the (stupidly massive) LED light on the front of the drive lit up. “Great” I thought! But no, the Mac was not seeing the drive, as far as it was concerned there was nothing connected. So I tried plugging the drive into the right hand side USB port and again it lit up, but this time it mounted on the desktop. Hmm… I unplugged it and tried the left hand side port again but the drive wouldn’t work.

As the drive requires 600mA according to Toshiba and the USB spec is supposed to be able to provide 500mA it would seem to me that my MacBook Pro (one of the first Core 2 Duo models) can provide 500mA to the left hand port, but it capable of providing more (how much more I don’t know) to the right hand port. My Western Digital drives work equally well in both ports, they say they require 500mA so I know the left hand port is providing that (ie is to spec) but it looks like the right hand port has that little extra…

Just in case my laptop was unusual I did some checking via Google and it seems that some manufacturers say their equipment must be used in the right hand port on the MacBook Pro, although they don’t say why. Apple claim both ports are the same but my experience and that of a few others on the Apple Discussion forums suggests the right hand port is capable of providing more power than the USB spec requires. Which is handy!

(I took the Toshiba drive back, the Western Digital drives work in either port, cost less and don’t have a cheap looking oversized LED light on the front)

Filed under: Computing