How to determine Operating System (Apple)
Help to determine OS version of an Apple computer
Apple - To find the version of OS X you have installed, use these steps:
- From the Apple menu, choose About This Mac.
2. The version number of OS X you're using appears directly below the words OS X.
You can also visit What my OS? website. This site will list your operating system at the top of the page. It will also give you directions to manually check OS version on older versions if necessary.