Also Read:-How to Install macOS High Sierra on VirtualboxOverview of Mac OS X El Capitan on Virtualbox on Windows. While downloading the package, MAS processes and converts it into an executable (.app) file, which can then be installed on your Mac. This raw file is not installable on its own. When you download OS X El Capitan using the Mac App Store, a raw package (.pkg) file is downloaded from the Apple server. How To How to install Mac OS X El Capitan on PC using VirtualBox