Editing GNU GRUB (section)

===Version 0 (GRUB Legacy)===
[[File:GRUB v1.5 Screenshot, Ubuntu 9.04.png|thumb|GRUB Legacy menu (running as part of [[Ubuntu (operating system)|Ubuntu]] 9.04 installation)]]
GRUB 0.x follows a two-stage approach. The master boot record (MBR) usually contains GRUB ''stage 1,'' or can contain a standard MBR implementation which [[chain loading|chainloads]] GRUB ''stage 1'' from the active [[Partition Boot Sector|partition's boot sector]]. Given the small size of a boot sector (512&nbsp;bytes), ''stage 1'' can do little more than load the next stage of GRUB by loading a few disk sectors from a fixed location near the start of the disk (within its first 1024 cylinders).

''Stage 1'' can load ''stage 2'' directly, but it is normally set up to load the ''stage 1.5.'', located in the first 30 [[KiB]] of hard disk immediately following the MBR and before the first partition. In case this space is not available (unusual partition table, special disk drivers, [[GUID Partition Table|GPT]] or [[Logical Volume Manager (Linux)|LVM]] disk) the install of ''stage 1.5'' will fail. The ''stage 1.5'' image contains file system drivers, enabling it to directly load ''stage 2'' from any known location in the filesystem, for example from <code>/boot/grub</code>. ''Stage 2'' will then load the default configuration file and any other modules needed.