How to Boot from USB on an Asus CM1855 UEFI Equipped Computer

My user recently bought two Asus CM1855 computers and asked me to install Windows 7 on them. I tried to boot the machine from a USB drive with my Windows 7 installation files. To my surprise, I could not select my USB drive as an option. This machine has the new UEFI firmware that I am not familiar with. After a bit of fiddling, I was able to figure out how to boot from the USB drive. Here are the steps:

  1. Turn on the power and press the DEL key immediately. You may need to press the DEL key repeatedly and make sure you see the UEFI screen. As you can see, only the internal drive is shown on the Boot Priority list even when I have the USB drive connected.
  2. Click on Advanced Mode
  3. Click on Boot, scroll down and change the OS Type to Other OS
  4. Press F10 to save settings and reboot.
  5. Press DEL again when the system boots up. The external USB drive is now an option to choose from. Press F8 to choose the USB drive to boot the machine from.

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