buffer cache

This is in the Series "100 Things You Probably Didn't Know About Oracle". If you haven't already, I urge you to read the other parts -

• Part1 (Commit does not force writing of buffers into the disk), 
• Part2 (How Oracle Locking Works), 
• Part3 (More on Interested Transaction Lists).

During the recently concluded Collaborate 11 (http://collaborate11.ioug.org) I was asked a question which led me to the idea for this entry - the fourth in the series. If the database size is 100GB and you have a 100GB buffer cache, all the blocks will be in the memory and there will never be an I/O to the datafiles other than the regular DBWR lazy writes, right?