If you hold down ‘T’ while booting a Mac, the screen will go black and display a large Firewire logo. In this state, called Target Disk Mode, your fancy laptop is magically transformed into a plain ol’ external hard disk. Connect it to another machine via a firewire cable and your Mac’s hard drive will appear on the other machine’s desktop, just as if you had connected an external firewire drive. Just unmount and reboot to return your trusty Mac to its normal self.
While turning your laptop into a $2000 firewire drive may seem a little bit of a downgrade, it can come in quite handy for transferring large files. Think about it: if you were to transfer a huge amount of data over sneakernet, you’d need to copy it over to a firewire disk, reconnect the disk to the another machine, and then transfer the data again over the firewire connection. With Target Disk Mode, you only make the firewire transfer once, so a large file transfer takes half the time. Like sneakernet, you still need to hike one of the Macs over to the other machine to make the connection, but since you are transferring half the data, you are only required to wear one sneaker.