With SolidWorks 2013, you now get the option to decide which version of SolidWorks you want to open your files.
Whenever you double-click on a SolidWorks file (part, assembly or drawing) in windows explorer (and SolidWorks is not running), you’ll get a pop up window asking you to choose which version you want to open you file with.
For e.g. if your machine has SolidWorks 2012 and 2013 installed, the pop window will prompt you to choose which version you want to open the file with. This is very helpful for people working with multiple versions of SolidWorks on the same machine. The option will help you to decide which version of SolidWorks you want to work with. This will also reduce the risk of saving a lower version file into higher version (though with the Previous Release Interoperability option you can open SW2013 file in SW2012 SP5)
Need more on what’s new in SolidWorks 2013, visit new SolidWorks 2013 website to see all the major updates.