Apple’s newest version of OS X Mountain Lion is only $19.95 and you can update all of your Macs without having to purchase it for each one. The way you get the new Operating System is through the Mac App store. The install is around 4 and a half GB and takes a considerable amount of time to download depending on your Internet speed.
So what do you do if you have a few Macs and don’t want to download it to each one? Easy. You create an install disk from the first computer you download it on.
You’ll need a writeable DVD, or a USB drive.
Then after paying for Mountain Lion and downloading the installer via the Mac’s built-in App Store hold off on running the installer. The reason you want to hold off is because you will want to copy the the installation process deletes the download installer once it’s done to save disk space. So if you want a bootable drive, hold off on clicking ‘Continue’ to install.
Open your Applications folder, right-click on the Install OS X Mountain Lion application and choose “Show Package Contents”. Browse into the Contents > Shared Support folder, and there should be a Disk Image called “InstallESD.dmg”. That’s the Mountain Lion install disk image.
Plug in your USB drive or insert your writeable DVD and launch Disk Utility, then drag InstallESD.dmg into Disk Utility. Format the drive you’re going to use as a single Mac OS Extended (Journaled) partition, clicking also on Options to choose GUID Partition Table, then choose Restore. The new partition is the Destination, and InstallESD.dmg is the Source. Click Restore, confirm your choice, and wait. About half an hour later your new bootable media will be done.