When you install windows 7 to a usb3.0 only pc you will found that you cannot move your mouse, keyboard after boot from cd, I tried intel’s usb3.0 tool but no luck, it does not support lenovo drivers, usb3.0 still doesn’t work after installation, and finally I found this :
Windows USB Installation Tool https://www.gigabyte.com/Support/Utility
Just download it, extract and run, Source Path by default - Add USB drivers, Destination Path - please point to your usb drive, stay the tick sign on Add USB drivers of an offline Windows 7 image, then click start, program will do it for you, it usually take 40 to 50 minutes to finish. I must say it here, good job gigabyte’s developer!