Per my understanding,

  • BIOS is the traditional boot method of Intel x86 computers. It starts by loading a short program called BIOS from somewhere on the motherboard (usually some EEPROM), which does a range of things like POST, before loading data the hard drive, including but not limited to further-stage bootloader codes.
  • UEFI is the new method of booting. It also starts with loading a small piece of code stored somewhere outside the main secondary storage (user hard drives), which also does a range of things before accessing hard drives.

The differences I'm able to tell so far:

  • BIOS loads something at a fixed location on a hard drive, specifically, the first 512 byte, called the master boot record, which loads everything further required to boot a OS.
  • UEFI doesn't load from a fixed location on hard drive. Instead it searches the partition table (GPT) and looks for a ESP (EFI System Partition) and find. .efi files inside and executes them.

The confusions I'm currently having:

  1. I've heard that in BIOS and UEFI, hardware initialization order is different and UEFI is usually a bit faster in this. How exactly is it?
  2. Is there any fundamental difference between BIOS and UEFI? To me, at the very basis, they both load the initial code from a piece of special hardware (a ROM) which does the necessary things before loading data from disk, which is a "fundamental similarity".


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