Difference between the Booting Process with UEFI and the Booting Process with BIOS

Booting Process With BIOS : When BIOS begins it’s execution, it first goes for the Power-On Self Test (POST), which ensures that the hardware devices are functioning correctly. After that, it checks for the Master Boot Record in the first sector of the selected boot device. From the MBR, the location of the Boot-Loader is retrieved, which, after being loaded by BIOS into the computer’s RAM, loads the operating system into the main memory.

Booting Process With UEFI : Unlike BIOS, UEFI doesn’t look for the MBR in the first sector of the Boot Device. It maintains a list of valid boot volumes called EFI Service Partitions. During the POST procedure the UEFI firmware scans all of the bootable storage devices that are connected to the system for a valid GUID Partition Table (GPT), which is an improvement over MBR. Unlike the MBR, GPT doesn’t contain a Boot-Loader. The firmware itself scans the GPT to find an EFI Service Partition to boot from, and directly loads the OS from the right partition. If it fails to find one, it goes back the BIOS-type Booting process called ‘Legacy Boot’.

Advantages of UEFI over BIOS

Breaking Out Of Size Limitations : The UEFI firmware can boot from drives of 2.2 TB or larger with the theoretical upper limit being 9.4 zettabytes, which is roughly 3 times the size of the total information present on the Internet. This is due to the fact that GPT uses 64-bit entries in it’s table, thereby dramatically expanding the possible boot-device size

Speed and performance : UEFI can run in 32-bit or 64-bit mode and has more addressable address space than BIOS, which means your boot process is faster.

More User-Friendly Interface : Since UEFI can run in 32-bit and 64-bit mode, it provides better UI configuration that has better graphics and also supports mouse cursor.

Security: UEFI also provides the feature of Secure Boot. It allows only authentic drivers and services to load at boot time, to make sure that no malware can be loaded at computer startup. It also requires drivers and the Kernel to have digital signature, which makes it an effective tool in countering piracy and boot-sector malware.

UEFI doesn’t require a Boot-Loader, and can also operate alongside BIOS, supporting legacy boot, which in turn, makes it compatible with older operating systems. Intel plans to completely replace BIOS with UEFI, for all it’s chipsets, by 2020.