The Multiboot specification is an open standard describing how a boot loader can load an x86 operating system kernel.
GNU Hurd, VMware ESXi, Xen, and L4 microkernels all need to be booted using this method.
The loader searches for a magic number to find the header, which is 0x1BADB002 ("1 bad boot") for Multiboot[5] and 0xE85250D6 for Multiboot2.
The ELF format is very common in the open source world and has its own field (e_entry) containing the entry point.
Before jumping to the OS entry point, the boot loader must provide a boot information structure to tell the OS how it left the system; for Multiboot, this is a struct, and for Multiboot2, every field (group) has a type tag and a size.