BIOS stands for “Basic Input Output System.” It is an old type of computer firmware that stays on the motherboard that controls hardware initialization and boot to OS.
There are four early Surface devices that use BIOS as their firmware including Surface Pro, Surface Pro 2, Surface 3, and Surface Pro 3. Starting with Surface Pro 4, the company no longer uses the BIOS firmware on Surface devices since it is slow and doesn’t supports newer security features. Instead, all newer Surface devices use a newer firmware called UEFI.
You can learn more about BIOS settings on Surface devices from the following resources: