What is meant by multiboot header?

Question

What is meant by multiboot header ? While going through the tutorials on how to make an OS. I came across this term.

Answer 1

Multiboot is about loading various kernels using a single boot loader. The Multiboot Header is a data structure in the kernel image that provides information to a Multiboot-compliant boot loader (GRUB for instance) about how and where to load the image, and which Multiboot features the image expects.

Answer 2

The multiboot header exists to allow a bootloader (for example, GRUB) to load the kernel to whom the header belongs in a way that that kernel expects.

For example, GRUB can provide the kernel with a memory map when it starts, but it would be a waste of time for GRUB to do that if the kernel it is loading won't use it. The flags field in the multiboot header is used to specify whether or not the kernel being loaded expects a map.

The multiboot header also includes the Multiboot magic number (which allows GRUB to find the location of the multiboot header).

In short, information in the header will either change how the kernel will be loaded into memory or request that the kernel would like some extra information.