How does a computer know where in the filesystem the bootloader is located? Is there a common file among all operating systems and all computers (maybe not all computers, but all architectures) that points to the bootloader? I know Raspberry Pi always loads bootcode.bin from the first partition of the SD card. Do PCs share a common file like this?
The Master Boot Record occupies the first 512 bytes of the first hard disk, and is the first thing loaded by the BIOS to hand over control to a program capable of booting the desired operating system. In general, a bootloader gets installed in the MBR, removing its previous content. It is (in dual boot cases) possible for them to live in co-existence, which is known as multi-booting.