Download: OS X El Capitan This downloads as a disk image named InstallMacOSX.dmg. On a Mac that is compatible with El Capitan, open the disk image and run the installer within, named InstallMacOSX.pkg. It installs an app named Install OS X El Capitan into your Applications folder. So, if you’re a typical Mac user, you really don’t need to enable the firewall. But, if you’re doubting the advice here or just feel better with it enabled, you’re also free to enable it. Typical Mac users probably won’t notice many (or any) issues after enabling the firewall. Before version 10, Apple used to call its Mac operating system Mac OS, with the last version being Mac OS 9. Apple change the name to OS X when version 10 was released in 2001. Apple just released its next-generation operating system for Macs, OS X 10.11 El Capitan, to the public. If you haven’t been using a developer or public beta version over the last few months.