Can anyone explain how that works? Surely there's a bottleneck on speeds at the PC/ card end?

USB isn't the only way of plugging external devices into a computer, after all...

Perhaps it uses simple, fast compression... but most 'big' stuff (audio, images, video) that people use at home is already compressed to death anyway, so that wouldn't give a huge improvement.

They could provide two USB cables and have you use two different ports on your computer, but they'd need to be on two different USB controllers. Not many machines provide more than one controller, I'd guess.

So I give up. Any other ideas?

if it's for Mac it'll be Firewire - 800Mbps, twice as fast as USB2.0

There are two typical ways to do that sort of thing. One is to compress the data as it goes out to the drive, ensuring hours of merriment when things go wrong in return for never knowing quite how big the disk is, effectively. It also further increases the CPU load associated with your USB devices, as if that wasn't already a problem.

The other is to violate some part of the spec. USB has rules about the priority of various sorts fo traffic, with "bulk", as usually used for storage devices, falling into the "whatever's left" slot of bandwidth. If a device claimed to be, say, a display or audio port, and used the isochronous slots, it could dial up the bandwidth pretty much as far as it wanted, killing the response of anything else on that controller. isochronous is not guaranteed delivery, but again, two choices, you could layer either forward error correction or a retry scheme on top, or you could just accept the occasional silently failing transfer, with resulting file corruption.

Any of these choices mean you need a "special" driver that hooks into the OS in "special" ways, so you would be very OS-specific (probably even OS-version specific). Note how carefully they say "Windows or Mac", then "Any PC". If they really mean the former, they don't mean the latter, and vice versa.

Is why I would buy the 1 TB for $500, when I could buy two 500 GBs for $340... Hell, you might even be able to set them up in a RAID array that way...

Turbo USB

Compression is the most likely answer, and 60% is probably achievable if you store massive text documents only.

Twice the power, Four times the failure rate?