ASUS T100TA - How I can install Windows 7
Solution 1:
Windows 7 needs BIOS INT10 to boot, in turn requiring CSM.
So, your only choice if you don't want Windows 8/10 is Linux. No need to even disable Secure Boot thanks to the Linux foundation shim most distros ship with.
There are also reported hacks to make 64 bit OS load.
EDIT: it turns actually out there exists hacks for booting without CSM!
EDIT2: UefiSeven has you covered completely now.
EDIT3: duh, the bay trail tablet has a 32-bit firmware, right. And that means W7 requires some extra meddling to work.