The BIOS, which stands for Basic In Output System, is a critical bit of low-level code stored in nonvolatile memory that your computer uses to manage your hardware and load Windows 10 or another operating system.
A new standard called UEFI or Universal Extensible Firmware Interface came online a decade ago and became the standard for new PCs and devices preinstalled with Windows 8 or later.
If you have a removable storage device set as your first boot device the BIOS will check if there is any attached removable storage as part of POST (Power On Self Test).
Once you’ve found the menu, the interface will present menus displaying the structure of your boot order.
Boot order determines which devices your computer will try to boot from first, second, etc. Most often, your first boot device is your hard disk or SSD containing Windows 10.
UEFI offers more advanced options than BIOS, with support for features such as a graphical user interface and mouse support, making it easier to configure boot and hardware settings.
UEFI also supports recent security standards required by Windows 10 and previous releases such as Secure Boot, which maintains the integrity of a computer’s state and prevents malicious code from compromising your system at boot time.