BIOS can run two types of firmware; legacy, or UEFI. UEFI is a modern, more secure firmware that newer systems run. There’s nothing complicated about it though, selecting a boot device in UEFI is a bit different than it is on Legacy BIOS. If you want to check if you installed Windows 10 in UEFI or Legacy BIOS, you can check the setup log files and find out.
Windows 10 Setup Log
This will work no matter how old, or how recent your Windows 10 installation is. Open the C drive, or whichever drive it is that you’ve installed Windows 10 on. Go to the following location but if you’ve installed Windows to a different drive, replace it in the address below;
Here, you want to look for a file called “setupact.log’. This is the setup log file that you can view with Notepad. Right-click it and select Open With from the context menu. Select Notepad from the list of suggested app. You can use other text editors if you want but Notepad is an option that’s available on Windows 10 out of the box.
Once you have the log file open, invoke the find bar with the Ctrl+F keyboard shortcut and search for the following;
Detected boot environment
Look at the value that is entered for it. If it says EFI, then your Windows 10 was installed from a UEFI BIOS. If it says BIOS, your system was installed running a Legacy BIOS.
It is possible to change the BIOS firmware after installing Windows, and changing it doesn’t have any impact on the operating system itself. That’s why it is entirely possible that your Windows 10 installation happened on one type of BIOS but you’re system is currently running a different one. It’s pretty easy to check in Windows 10 which is the current BIOS firmware type.
If you find that you’re running a different type of BIOS firmware and Windows 10 was installed using a different one, it’s not an error. It is entirely possible that whoever installed Windows 10, opted to use a different BIOS to do it. We should mention that while it’s pretty easy to change the BIOS type later, i.e., after Windows 10 has been installed, doing so before installing Windows 10 isn’t a good idea unless you’ve already set up your disks for it.
UEFI requires the GPT partition table to be used on disks whereas Legacy BIOS works with MBR. If you don’t know what either of those things are, it’s best to use the BIOS that is currently configured.