If I use Time Machine to backup all the data...for all users, and the settings on my MacBook pro, my understanding is that I would be able to recover that information in the event I needed to restore that information. However, if the computer hard drive fails to function and I have to replace the hard drive (the operating system at this time is Yosemite 10.10.2) I am assuming that I would replace the hard drive with a new hard drive. How do I replace the operating system as I do not have any disc for the OS called Yosemite? Do I just go to the Apple Store and download Yosemite and install it? I am assuming that my Apple ID would make this possible but I am not sure. Also, one related question...is it possible to do a system image of the hard drive with Time Machine? My impression is that Time Machine is good at backing up data but the folks who talk about Time Machine do not promote doing a system image with that software.