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Things you’ll need: a trial copy of TransMac, a USB flash drive with at least 8GB of storage (16GB is recommended), and a copy of OS X (DMG file). Now that you have all the necessary ingredients, you’re ready to make a Mac OS X bootable USB using the DMG file of the operating system with the steps below.
Instructions
Download and install a copy of TransMac, which is the software that will make everything happen. TransMac is a paid software, but it has a 15-day trial solution, that give us more than enough time to move the DMG files to the USB drive from Windows. (Though, if you want to support the developer, you can purchase the full version.)
Insert the USB drive that you’ll use to fix your installation of OS X. Remember that all the data in the USB will be erased. Make sure you take off any important documents.
Right-click the TransMac software icon and Run as administrator. You’ll be prompted to Enter Key or Run because we’ll be using it once, click Run.
On the left pane, you’ll see all the Windows PC drives listed, right-click the USB drive you’re intending to use to re-install Apple’s OS and click Restore with Disk Image.
In the warning dialog box, click Yes.
Use the Restore Disk Image to Drive dialog box to browse for the DMG file with the installation files for Mac OS X Yosemite in this case, and click OK to create a bootable USB of the operating system.
Now, you’ll have to wait a long time. No kidding. It could take one or two hours to complete the process depending on your computer and other variables.