My iMac has been going super slow for the past few days, so I decided to restart it. When restarting, I had it install a software update which was only a couple hundred megabytes, but took several hours to install. So I'm fairly certain my hard drive is beginning to fail (constant beachballs, etc.). It's not always THAT slow, but it has its good moments and its bad moments. So my question to you hard drive experts out there is, considering how slow my computer is now acting, is it likely for me to able to do a full system back up in Time Machine (my internal drive is 500GB and full), or would I be lucky to back up just a few important files? And considering my symptoms, how much time (if you had to guess) would you say I might have before complete drive failure? ANY input would be greatly appreciated, I'm at the point where I'm terrified to turn my iMac back on for fear of it instantly failing. Thanks.