I have clean installed two laptops now, with Windows 10: An Asus laptop and a Lenovo laptop. However, for both installs — I noticed that the PC’s still display the Asus loading image when booting and the Lenovo loading image when booting respectively.
I initially thought the clean install wipes the whole laptop, but on second thought, I do not think it wipes the UEFI/BIOS. So my question is:
in modern computers BIOS/Firmware (UEFI) code are stored in a chip (an EEProm) attached to the motherboard. The Windows install exists on your hard disks. When you install, you wipe out the hard disk, but the BIOS is untouched.
Source: http://www.knowcomputing.com/bios/
If you were to wipe out the EEProm, the motherboard would stop working until you sent it back to the manufacturer to have the software "flashed" back onto the chip. Your motherboard is simply an expensive paper-weight without its BIOS code. It can't POST or boot.
The BIOS contains code specifically for that motherboard, so you cannot install a different BIOS, except for manufacturer upgrades. As John noted, the POST logo image is part of the BIOS code.
I've added custom images to fireware before. generally they must be bitmaps of a fixed resolution and aspect ratio, so that the data footprint of the image on the chip is predictable. you have to change the image during a flashing operation in order to update the logo image.
