Since yesterday I messed up the MBR section of the harddisk when installing Ubuntu, it cost me a whole night removing/repartitioning/replacing hard disks from macbook pro and pc laptop, also I only have a 8GB usb stick so not all data can be backed up, I decided to buy an external hard disk for time machine. I am not familiar with this and have some questions: 1 What can it backup? Whole disk, everything? Only documents, music and video? Or I can select what folder to backup? What about certificates(I use XCode for iphone development)? 2 Does it backup whenever a file is modified(so there is several copies of one file at different time)? Or only the latest version of a file is backed up? I have a 160GB harddisk, how much quantity of the external harddisk do I need for this? 3 Do I have to use Apple's time capsule only? Or I can use any other brand? If so, which brand is the best? Thanks a lot!