I know, does this guy not know that you dont have to defrag OS10? Ive read all the info on the subject, but I have another question nevertheless. I do a lot of video work on my iMac, files in excess of 250mb, adding..deleting..modifying, etc. I have read that this OS will automatically defrag files of approx 20mb or less. With the work I do on my iMac, and the size of the files I move around my HD, should I be concerned about the need to defrag my computer? And if so, what 3rd party software? Thanks.