BIOS (Basic Input Output System) and UEFI (Unified Extensible Firmware Interface) are two frameworks motherboards use to boot systems. BIOS is a classic framework, while UEFI is a modern framework.
BIOS is stored on a read-only flash memory chip called EPROM (Erasable Programmable Read-Only Memory). EPROM is a non-volatile chip. It retains its contents even after the power is turned off.
When we start a system, BIOS is the first program the system runs. BIOS checks all connected devices and initializes them. This process is called POST (Power On Self Test). After performing POST, BIOS selects the bootable device, reads the boot code from the selected bootable device's MBR, and executes that.
BIOS works in 16-bit mode. The 16-bit mode limits the amount of code that can be read and executed. Due to this limitation, BIOS recognizes and supports storage devices up to 2 TB. If you have a hard disk bigger than 2 TB, the BIOS-based system will not recognize it.
UEFI (Unified Extensible Firmware Interface) is low-level software. It was developed to address the limitations of BIOS. It works similarly to BIOS but supports storage devices of all sizes and many modern features that make framework management easier and more secure.
It works in 32-bit and 64-bit modes. It can boot from a disk larger than 2 TB. It provides a graphical user interface, which is easier to use than the old terminal interface in BIOS.
Differences between BIOS and UEFI
The following table lists the differences between BIOS and UEFI.
| Feature | BIOS | UEFI |
| Operating Mode | 16-bit | 32-bit and 64-bit |
| Release Date | 1975 | 2002 |
| User Interface | Only basic UI navigation using the keyboard | Provides a user-friendly graphical UI with mouse support. |
| Partition Support | Up to 14 | Up to 128 physical partitions |
| Partition Size Limit | 2 TB | 18 exabytes |
| Performance | slower boot times | faster boot time |
| Storage | It stores system initialization information on a dedicated chip on the motherboard. | It stores system initialization information in a .efi file on the hard disk. |
| Security | It supports password protection. | It supports secure boot features. |
