I'm wondering what happens when the disk contents change during a backup. For instance, suppose True Image has already copied the sectors for Outlook.pst to the backup image, then I receive a new email so Outlook writes to that file. Does True Image somehow keep track of what sectors are updated during the backup then go back later and re-write them to the image? Or, will the backup image just contain the old copy of Outlook.pst that doesn't contain that new email? Now for a worse situation - what happens if True Image has backed up half the sectors of a file and then an application writes to that file? Do I end up with a corrupt file in the backup? How does True Image handle this? Does it lock files while it is writing them? If so, what if the file is already locked by an application? I'm asking these things because: 1) I'm a geek and I like to know how things work. 2) I need to know if it's best to shut down all applications while the backup is in progress, or whether it's safe to keep working.