Hi All, I have a June 2010 17" 2.66 i7 UMBP which has a 500GB internal HD. I recently purchased an external HD of the same capacity so I could keep a full back up of all my data. The internal HD shows capacity of 499.76GB with 160.24GB free. After connecting the external HD to the UMBP & doing a back up via Time Machine, it shows capacity of 499.76GB with 166.99GB free. This means there is a difference of 6.75GB between my internal HD & the back up one which to me seems a large amount. I can only assume that Time Machine has not backed up this missing 6.75GB of data & would like to know why this is so & what I can do to correct it. I have run Time Machine again a few times but the numbers still stay the same. Please can anyone else help me out here as at present, I just do not feel comfortable with they way things are & there is no way I can tell what data is missing on the back up HD - my luck is that it will probably be something(s) that might be important/critical in future! Many Thanks, Bazzy!