I'm about to purchase my first Mac and I'm trying to think through all the things that'll be different. I've always used some type of image backup software for Windows - currently Acronis TruImage. I make an image backup of my entire computer which results in one big file being created. When I'm in Windows, if I want to pull out just one file from that image, I can browse the image from the Acronis software. Easy. With Time Machine, I understand that you connect an external hard drive and the system will create an initial image backup. After that, it creates hourly/daily/weekly/monthly incremental backups automatically. You then use the Time Machine interface to "go back in time" and pull a file out from whenever you need it. Couple of questions: 1) Does the external hard drive have to be dedicated to Time Machine? I currently have a 1.5 Tb external USB hard drive that I use for making image backups of my various computers in the house. 2) Let's say I upgrade to a future version of OSX and decide to do a clean install instead of an "update". When I get the OS installed, can I then start pulling files out of my old Time Machine backup? Or is Time Machine going to start backing up the newly installed Operating System to the external disk?