

This guide assumes you are installing Windows on your computer for the first time.
What You Need
You will, of course, need Windows 10, which can be purchased from Microsoft for $119. Older Mac computers support older versions of Windows, but won't work with Windows 10.
Make sure to check the system requirements for the version of Windows you want to install to ensure your Mac meets or exceeds them. You can find out the system specs for your Mac using System Information, accessible by typing "System Information" into a Spotlight search or using the Apple menu to go to About This Mac --> System Report.
To install Windows 10 (or Windows 7 or 8 for that matter) you will need at least 30 GB of free space on your startup drive and you'll need a keyboard and a mouse or trackpad to use with your computer.
If you're running OS X El Capitan and have an 11- or 13-inch MacBook Air, a 13- or 15-inch MacBook Pro or the Mac Pro, there's no need for a USB drive. If you're running a different version of OS X or have an older Mac, you'll need a 16 GB flash drive that doesn't have anything you don't want erased on it (Boot Camp Assistant automatically reformats the flash drive).
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Article Link: How to Install Windows 10 on Your Mac Using Boot Camp Assistant