Does my Time Machine backup disc need to be dedicated? I have an external HD that's about 60% full. The remaining space is more than enough for a Time Machine backup of my hard drive. If I enable Time Machine using that disc, will it erase my existing files, or just use the free space?
If you want an encrypted backup, Time Machine will erase the contents on the drive as part of the encryption process. (It is a full disk encryption.) In that case, yes, you'll need a dedicated blank drive.