I'm trying to understand how the boot process works and the differences that exist between legacy BIOS and UEFI, but when it comes to the video BIOS, I can't find much information except a small article on Wikipedia.

As for my understanding, the video BIOS's main job is to provide a basic interface for displaying characters and 2D images during the boot process.

However, I can't find an answer to the following questions:

  1. Wikipedia says that BIOS/UEFI loads the video BIOS early in the boot sequence, but it also says:

    The system BIOS loads the video BIOS from the card's ROM into system RAM and transfers control to it early in the boot sequence.

    Does that mean that the rest of the boot process is actually executed by the video BIOS, and not the motherboard's BIOS/UEFI? Or does it mean that the video BIOS, after being loaded, once it finishes to do something (what exactly?), transfers control back to the system BIOS/UEFI, which then completes the boot sequence?

  2. Is there such a thing as video UEFI, as opposed to video BIOS?

    I often see GPUs that claim to be UEFI-ready, but I don't understand what does that really mean (besides the fact that a non-UEFI-ready GPU isn't compatible with a UEFI system. But why?)

Is the difference between a video UEFI and video BIOS the same existing between a motherboard's legacy BIOS and UEFI? (which wouldn't make much sense if the video BIOS/UEFI isn't in charge of completing the boot sequence) Or is there something else that I'm (probably) overlooking?

  • The transfer of the video is for a software operating system like Windows to start the loading of the video drivers. I am not aware of any difference with UEFI or BIOS as far as the video goes. BIOS starts with a normal VGA and allows the OS to take over to whatever the system needs. Special drivers for the video card, etc. GPU's being UEFI-ready, I think, means the compatiblilty of the BIOS. – vssher Jun 8 '20 at 0:36
  • @vssher Wikipedia states that the video BIOS is given control early in the boot process, when there is no OS loaded at all. – Maury Jun 8 '20 at 0:53
  • No matter how early the operating system which takes control still has to configure and talk with the BIOS, be it UEFI or legacy BIOS all information has to go through the BIOS to communicate with the hardware. The BIOS is controlling the motherboard. – vssher Jun 8 '20 at 1:06
  • @vssher sorry, I'm not following. I'm starting from the assumption that during the boot process, the CPU can only run one program at once. If control is given to the video BIOS, how can the motherboard's BIOS/UEFI complete the boot sequence? Besides, you seem to be only focusing on the OS, but from what I know the video BIOS is also used to display things like the BIOS/UEFI's user interface. – Maury Jun 8 '20 at 1:48
  • If you could make an answer addressing my questions and explaining in detail how the video BIOS fit in the entire boot sequence, I'd be glad. – Maury Jun 8 '20 at 1:55

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