<P> GNU GRUB was developed from a package called the Grand Unified Bootloader (a play on Grand Unified Theory). It is predominantly used for Unix - like systems . The GNU operating system uses GNU GRUB as its boot loader, as do most Linux distributions and the Solaris operating system on x86 systems, starting with the Solaris 10 1 / 06 release . </P> <P> When a computer is turned on, BIOS finds the configured primary bootable device (usually the computer's hard disk) and loads and executes the initial bootstrap program from the master boot record (MBR). The MBR is the first sector of the hard disk, with zero as its offset (sectors counting starts at zero). For a long time, the size of a sector has been 512 bytes, but since 2009 there are hard disks available with a sector size of 4096 bytes, called Advanced Format disks . As of October 2013, such hard disks are still accessed in 512 - byte sectors, by utilizing the 512e emulation . </P> <P> The legacy MBR partition table supports a maximum of four partitions and occupies 64 bytes . Together with the optional disk signature (four bytes) and disk timestamp (six bytes), this leaves between 434 and 446 bytes available for the machine code of a boot loader . Although such a small space can be sufficient for very simple boot loaders, it is not big enough to contain a boot loader supporting complex and multiple file systems, menu - driven selection of boot choices, etc . Boot loaders with bigger footprints are thus split into pieces, where the smallest piece fits into and resides within the MBR, while larger piece (s) are stored in other locations (for example, into empty sectors between the MBR and the first partition) and invoked by the boot loader's MBR code . </P> <P> Operating system kernel images are in most cases files residing on appropriate file systems, but the concept of a file system is unknown to the BIOS . Thus, in BIOS - based systems, the duty of a boot loader is to access the content of those files, so it can be loaded into the RAM and executed . </P>

The history on boot loader for linux what is the default boot loader currently for linux