Using an external drive to install Mac OS X Mountain Lion can save some time if you have to install the operating system on multiple computers. You’ll need to purchase a license for each computer you are using, but you can use the same installation software on each computer. This prevents the need to download Mac OS X Mountain Lion from the Apple servers each time you want to install the software. You can also use an external drive to do a fresh installation of Mountain Lion on a hard drive that doesn’t have the Mac OS X Recovery partition installed. Writer Bio
