I am new to the MAC World and have a couple of questions. The iMac I have is in my signature. So far I am pretty happy with it I have installed a whole host of applications and then uninstalled some. Also copied large/small files (movies, music etc...) on to my HD and then deleted them. So, I am a little concerned about defragmentation on my HD. I know that MAC OS X is supposed to be pretty good with file allocation, but I would like to "defrag" my HD by formatting and reinstalling the OX. Am I right in thinking that when the OS reinstalls it will be all contiguous and not have any gaps between the data? hence no need to defrag? Most Importantly, can I back up my OS with all the applications and reinstall it from the back up with all the applications that I have on my iMac???