I back up my PC, say once a week, on to an external Hard Drive using the Vista Back Up and Restore centre. I have almost filled my 320GB external drive, but my internal HD still has plenty of capacity. I was expecting the internal and external drives to almost mirror one another in terms of capacity used, as I only use the external HD for backing up this PC. Please could someone advise me where I am going wrong, and provide me with some useful info. in order to reclaim some of the external drive's capacity and manage my backups better in the future. Thank you for your help.