An ExpressCard34 USB 3.0 card and drive can work on MacBookPros with this slot when the machine is natively Windows7 (i.e.via Bootcamp, not as a VM machine within a virtualisation software running on MacOS) with at least a significant speed advantage over USB 2.0

Start your read from:
"I used the PC Card on a MacBook Pro running BootCamp with Windows 7 64 Bit Home Edition"
http://www.bonafidereviews.com/review-of-blackarmor-ps-110-usb-3-0-performance-kit/

This would indicate that the hardware on a MacBookPro would support an ExpressCard34 USB3 expansion card and harddrive since this review states this when the machine is running Windows7 natively i.e. on Bootcamp.

So any incompatibility of using such a setup with a Mac on OSX is purely software, i.e. OSX does not have the drivers.

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