Here's how you can free up inactive memory in OS X.
1. Open a terminal window.
2. Type in the following command, then hit Enter. purge
3. Check the Activity Monitor app before and after you do this.
Notice how the free memory in System Memory changes after you run the purge command.
For more, see the original article at the link below.
5 Essential Time-Saving Tips for OS X Mountain Lion | TechnoDuet