D.1 The memory map of various components

GRUB consists of two distinct components, called stages, which are loaded at different times in the boot process. Because they run mutual-exclusively, sometimes a memory area overlaps with another memory area. And, even in one stage, a single memory area can be used for various purposes, because their usages are mutually exclusive.

Here is the memory map of the various components:

0 to 4K-1

BIOS and real mode interrupts

0x07BE to 0x07FF

Partition table passed to another boot loader

down from 8K-1

Real mode stack

0x2000 to ?

The optional Stage 1.5 is loaded here

0x2000 to 0x7FFF

Command-line buffer for Multiboot kernels and modules

0x7C00 to 0x7DFF

Stage 1 is loaded here by BIOS or another boot loader

0x7F00 to 0x7F42

LBA drive parameters

0x8000 to ?

Stage2 is loaded here

The end of Stage 2 to 416K-1

Heap, in particular used for the menu

down from 416K-1

Protected mode stack

416K to 448K-1

Filesystem buffer

448K to 479.5K-1

Raw device buffer

479.5K to 480K-1

512-byte scratch area

480K to 512K-1

Buffers for various functions, such as password, command-line, cut and paste, and completion.

The last 1K of lower memory

Disk swapping code and data

See the file stage2/shared.h, for more information.