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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.
Don't forget that if you don't want to shutdown the machine you can use firewire between two Macs to create a network. (Although it probably requires more configuration to share files.)
I can only find a cached article on the Apple site describing it:
http://www.google.com/search?q=cache:docs.info.apple.com/article.html%3Fartnum%3D152307
--Phil.
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This is a pretty old feature (is something that's documented truly a "hack"?) and I can sort of remember doing the same thing on my old PB3400c, but in that case you were able to make it a SCSI "target."
That being said, it's a pretty useful thing to know how to do.
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Very handy when your optical drive has failed. You can do your major OS upgrades by being a target drive and doing the install from the other machine.
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If you have MacDrive software on your Windows computer you can mount the whole Mac on a Windows computer when in target disk mode.
Very handy if you need to go cross-platform.
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its really handy for data recovery. its seems to work even if you've managed to mess up an upgrade to leopard and left your laptop unbootable.
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Yes, as D. Feather said, this has been a fully documented Mac feature for at least 15 years (with SCSI preceding Firewire.) Just another well cooked Easter egg for you PC switchers, I guess.
And yes the feature functions even if the system and other software on the machine posing as a firewire drive is totally FUBAR'ed. The feature is in firmware.
BTW, this will work on ALL Macs, not just laptops. I.e., Minis, desktops, etc. You may think, "why would I want to plug my desktop into my laptop (or another desktop) as a Firewire hard drive, but then start thinking about data recovery options, trouble shooting, System reinstalls, etc.
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Can you do the opposite - that is make the Windows machine a target disk on the Mac machine to allow an easy transfer of files?
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