Create a Windows Install USB on OS X Yosemite

Microsoft would have you believe that you need a computer running Windows 7 or later to create a USB install disk for Windows. Unfortunately, this makes no fucking sense at all - if I’m already running Windows on my machine, what do I need an installer for? Fortunately, not everything Microsoft tells you is true.

Creating a Windows installer from OS X is actually quite simple - Boot Camp Assistant can do it for you. If you’re on a newer machine without an optical drive, you probably have an option that says “Create a Windows 7 or later version install disk”. Click that and point it to your ISO image. Done.

If you’re on an older machine (like my Hoth), you won’t find this option. Don’t Panic! Hacking Boot Camp Assistant into small bits and reassembling it will do the trick.

First of all, we’ll modify BCA’s Info.plist. It’s at /Applications/Utilities/Boot Camp Assistant.app/Contents/Info.plist. Open it in your favorite text editor (Note: this requires elevated privileges). Once we’re there, we’ll tell it which machines can create USB disks. Look for the key PreUSBBootSupportedModels. Change it to USBBootSupportedModels. Makes sense, right? Save.

Then, we’ll need to resign BCA, otherwise it will refuse to run. For this, we’ll need the Xcode command line tools installed. Then it’s as easy as

sudo codesign -fs - /Applications/Utilities/Boot\ Camp\ Assistant.app

Now restart BCA, and you’ll find the option you were looking for.