Before you upgrade to Mavericks consider this. I have not been able to get time machine to work properly after upgrade. I even tried throwing away most of my data (backed up elsewhere of course) and no luck. Time Machine either backs up very slowly or not at all. I also encountered problems where the backup would stop entirely when the compute went to sleep. Also, and I know this is kind of an exotic set up, by I have a LaCie ESATA to Thunderbolt port adapter set up to a docked bare hard drive. This setup managed to destroy two Time Machine back-up disks. Disk read and write errors began to happen and eventually the drives were unusable. I was using this setup for months prior with no problems. My machine in question is: Model Name: iMac Model Identifier: iMac13,2 Processor Name: Intel Core i7 Processor Speed: 3.4 GHz Number of Processors: 1 Total Number of Cores: 4 L2 Cache (per Core): 256 KB L3 Cache: 8 MB Memory: 32 GB Also note that I installed Mavericks on a mid-2010 MacBook Pro and I don't have the same problems with Time Machine. There is no Thunderbolt port on that machine so it is not possible to test there. Apple was very helpful and tried to collect system data to help troubleshoot but that didn't work and in the end it was easier for me to kill the hard drive and reformat to Mountain Lion. I would be very careful about installing this OS, especially if you have any kind of valuable data on it and you use Time Machine to back it up. Time Machine works great and it has saved my life many times. Having it broken or in question was too much of a risk for me to take. I would take a look at the Mavericks discussion group to see what kind of experience people report before you upgrade. I got so excited by "free" that I didn't wait and see before I installed.