I had a left over 750GB hard drive from a 2012 MacBook Pro 13" after switching it out with an SSD drive - this 750 GB drive had 10.8 pre-installed from the factory. I also had a 2010 15" Macbook Pro running OS X 10.6 on a 500GB drive, running out of space. I wanted to get a larger drive in the 15" 2010 model, and also wanted to upgrade it to 10.8, so I thought I would try installing the left over 750 GB drive from the 2012 model. Everything went smoothly - I installed the drive and everything is working. But I'm wondering if this was the smartest move. Are the OS's that are installed from the factory all identical, or are the custom made for specific models - e.g. are drivers left out? Should I start over with a completely fresh install on the 750 GB drive, and not reuse an OS that is intended for another hardware model. The computer seems a bit slow, but this could also be attributed to spotlight reindexing the entire drive. Any thoughts?