As to the usual, I'd be guessing if you meant Target Disk Mode. More at
About 2years ago I read hint in Mac World mag about how to make the HD on an iBook appear on the desk of my iMac. I connected the iBook to the iMac using a cable, then booted the iBook. I held down a certain key on the iBook, but for the life of me I cannot remember the key. I would appreciate any help.