The difference between BIOS and UEFI

BIOS and UEFI are two types of firmware used to initialize hardware and load the operating system during computer startup. When you need to install or reinstall an operating system, change hardware configuration, or perform system repairs, you often need to consider the computer's boot mode and choose whether to boot from BIOS or UEFI. Therefore, understanding these two concepts and their differences is helpful for daily maintenance and system deployment.

BIOS， The full name is Basic Input Output System, which is a set of programs embedded in the read-only memory chip of a computer motherboard. Strictly speaking, the term 'read-only' referred to here is not entirely accurate, as will be further explained later. BIOS controls all hardware resources on the computer, mainly responsible for initializing, detecting, calling hardware devices, and starting the operating system. Generally speaking, after pressing the power button, quickly pressing the enter key, F2 or Delete key can enter the BIOS system, and the operating methods may vary for different brands of computers.

BIOS was born in the 1970s and runs in 16 bit real mode. With the upgrade of mainstream computer operating systems to 32-bit and 64 bit, the design framework and basic functions of BIOS are no longer able to meet the more boot requirements of computers, thus UEFI has emerged.

UEFI， The full name is Unified Extensible Firmware Interface, which is a computer firmware interface standard published by the UEFI forum. It is responsible for hardware boot, system diagnosis, and operating system startup after computer startup. Compared to BIOS, the main advantages of UEFI are its ability to support large capacity hard drives, especially 2TB and above, support UEFI user interface, shorter boot detection time, and easier firmware code maintenance. Currently, most computers have replaced BIOS with UEFI.

There are significant differences between different motherboards in terms of BIOS and UEFI interfaces, but most motherboards provide Legacy, which is the traditional way of booting, namely BIOS mode and UEFI mode, and users can freely switch between them.

As mentioned earlier, BIOS and UEFI are two types of firmware used to boot the system. They are stored in a read-only chip on the motherboard, but this read-only is not completely read-only, but a special, erasable flash memory chip.

In early computers, BIOS was indeed burned onto read-only memory (ROM) chips, and once manufactured, it could not be changed. But with the development of technology, firmware chips have undergone the following evolution. The read-only memory ROM is written in one go through photolithography technology during the chip manufacturing stage, and can only be read and cannot be changed after leaving the factory. Programmable read-only memory (PROM) is written once through a high-voltage programmer after chip manufacturing and cannot be erased thereafter. EEPROM, an electrically erasable programmable read-only memory, can be erased and rewritten on a circuit board using specific voltages, but it is slow in speed. Flash Memory is a chip commonly used in modern BIOS and UEFI firmware, which can be quickly erased and rewritten.

The BIOS and UEFI firmware on modern motherboards are burned onto flash memory chips, which can be rewritten. And the "read-only" mentioned earlier refers to the fact that the CPU can only read instructions relative to the runtime CPU to ensure the safety of program execution; But from the perspective of design, manufacturing, and maintenance, it is a rewritable flash memory that facilitates manufacturers and users to upgrade, that is, to flash BIOS and perform firmware upgrades.