I’m really excited about the Windows Technical Preview (aka Windows 10) that was released today. I decided to forgo a virtual machine and dual-boot it on my laptop running Windows 8.1. My laptop is an Asus G55VW and the existing Windows 8.1 installation being setup in UEFI (with the requisite GPT partition scheme).

I downloaded the image and made a flash drive using the Windows 7 USB Download Tool, but when I booted from the drive and tried to install, I got an error message: “Windows cannot be installed to this disk. The selected disk is not of the GPT partition style” when I clicked on the empty partition I wanted to install to.

I realized the flash drive was booting the MBR installer, but I needed UEFI. I realized I needed a USB flash drive setup to boot the Windows Technical Preview installer in UEFI mode. Here’s what I had to do to create the bootable flash drive that does just that:

1. Plug a flash drive into a USB port on your machine.
2. Download the Windows Technical Preview 64 bit ISO at http://preview.windows.com (you’ll have to join the free Windows Insider program and click through a few screens to get to the download link)
3. Download Rufus. Rufus is a small utility that will put the ISO files on a flash drive you can use to boot from and install Windows. While there are other utilities that do this, Rufus allows you to specifically setup the flash drive as a GPT boot device. This will allow you to install Windows Technical Preview on a GPT drive, side-by-side with Windows 7/8/8.1.
4. Launch Rufus.
   1. Set the Device dropdown to the flash drive you want to turn into a technical preview installer.
   2. Set the Partition scheme and target system type dropdown to GPT partition scheme for UEFI computer.
   3. Click the little disc icon next to the ISO image drop down and point to the Technical Preview ISO you downloaded in step 1.
   4. Click Start and wait until the status says DONE.

Setup Rufus as shown, using the Windows Technical Preview ISO as the source image

You should now be able to boot from the USB drive and install the 64 bit Technical Preview in dual boot on most machines that boot using UEFI and have a hard disk with GPT. I’ll leave it to you to find out how to create a empty partition to use for the installation, but at least now you will have a UEFI flash drive installer.