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BIOS vs UEFI. Are you confused about UEFI, BIOS?

BIOS – basic input output system.

UEFI – Unified Extensible Firmware Interface


BIOS is a low-level software located on the motherboard. Manufacturer saved BIOS software inside the BIOS ROM or BIOS IC or BIOS chips.

The BIOS instructions are the first set of instructions executed by the processor on the computer. BIOS performs a test, before booting your operating system. The test is known as the Power On Self Test (POST). during POST, it checks all the hardware connected with the motherboard that is properly configured and worked. BIOS helps to boot the computer. After performing POST, BIOS looks for MBR, to load the OS on the computer. MBR means Master Boot Record.

CMOS and BIOS work together. All the BIOS configuration settings are saved automatically on the CMOS.


UEFI is the modern version of older BIOS. Now PC manufacturers use modern UEFI instead of traditional BIOS. Modern UEFI overcomes the various limitation of older BIOS. Like BIOS, UEFI helps to boot a computer. UEFI provides more advanced features to the computer such as user-friendly interface, booting speed & performance, booting drive size, etc.

A firmware is a set of instructions or programs saved on ROM. Intel started to work on Extensible Firmware Interface (EFI) to replace BIOS. Intel owns EFI specification and the UEFI forum owns the UEFI specification.


1. Booting:

BIOS first performs POST. After successful completion of POST, it checks MBR and, retrieves the boot loader. After loading the boot loader to RAM, it loads the OS into the main memory. UEFI uses EFI service partition to boot and load OS from the right partition. UEFI uses GPT (GUID Partition Table) to find EFI service partition. GPT has a separate dedicated EFI System Partition(ESP) for storing multiple bootloaders. In UEFI we don’t need a separate boot loader. During the POST procedure, the UEFI firmware scans all of the bootable storage devices that are connected to the system for a valid GPT.

2. Size limitation:

BIOS uses MBR to save information about the hard drive. UEFI uses GPT to save information about the hard drive. BIOS can use a maximum of 4 primary partitions, but GPT can have more than 4 primary partitions. In BIOS maximum partition size is 2TB, but in UEFI maximum partition size is 9.4ZB(Zettabyte).

3. Booting speed:

BIOS runs in 16bit processor mode but, UEFI can run 32bits or 64bits mode. Therefore, in UEFI boot process is faster than the traditional BIOS.

4. Secure boot:

BIOS does not offer any secure mode but, UEFI offers secure boot to prevent boot-time viruses from loading.

5. User-friendly interface:

UEFI provides a better user interface(UI) than BIOS. Users can use both keyboard and mouse to configure UEFI but in BIOS users can use the only keyboard.

Intel plans to completely replace BIOS with UEFI, for all it’s chipsets, by 2020. UEFI can also work with old BIOS specification by using Legacy Mode. UEFI has a feature of backward and forward compatibility.