can I export a laptop's partition as an external HD?

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http://www.linuxquestions.org – Hello list. I'm wandering if it is possible to set up a partition on a laptop's HD so that if I use a USB cable between it and another device, the partition would appear as an external HD on the device. Old Mac laptops used to have the option at boot-time of sharing the hardrive via firewire (they might still have it, have no clue) I'm looking for something similar, but on a laptop with Linux running on a different partition. Cheers, R. (HowTos)