The F2 key will get you into the Phoenix BIOS. The main screen above shows the DOM on in the IDE interface on the motherboard, and the IBM drive that I have fitted in the drive bay.
The boot options are shown on the right. It took me a while to sort it out but, having selected a
particular entry, you use the F5 and F6 keys to move it up/down
the priority list.
The M100 runs Windows XPe.