What is it? When you put your PB into sleep mode, the function Safe Sleep automatically saves the contents of RAM memory (desktop settings, open applications, and other work in progress) to the hard drive; it prevents any data lost due to potential power failure when your computer is in sleep mode.
To test this function, turn your new PB into sleep mode, wait few seconds (till you do not hear the HD), then remove the battery. Wait until the flashing diode stops emitting (plenty of time to place a new battery), then place back the battery, and open up your notebook. You should see the following screen for a couple of seconds:
It displays the same windows/desktop as it was before turning the computer into sleep mode, while featuring a progression bar in the lower partof it, translating the recovery process of all information from the saved info on the HD and their transfer back into the RAM. It is a really fast process.
For more information related to this feature, read :
http://docs.info.apple.com/article.html?artnum=302477
