X86 memory Arrangement

Physical memory layout of the PC

Linear address range	Real-mode address range	Memory type	Use
0-3ff	-0000: 03ff	Ram	Real-mode interrupt vector table (IVT)
400-4ff	0040: 0000-0040: 00FF		BIOS data area (bytes)
500-9 fbff	0050: 0000-9000: fbff		FreeConventional memory(Below 1 MEG)
Fc900-9 FFFF	9000: FC00-9000: FFFF		Extended BIOS data area (EBDA)
A0000-bffff	A000: 0000-b000: FFFF	Video RAM	VGA framebuffers
C0000-c7fff	C000: 0000-c000: 7fff	Rom	Video BIOS (32 K is typical size)
C8000-effff	C800: 0000-e000: FFFF	Nothing
F0000-fffff	F000: 0000-f000: FFFF	Rom	Motherboard BIOS (64 K is typical size)
100000-febfffff		Ram	FreeExtended memory(1 Meg and above)
Fec00000-ffffffff		Various	Motherboard BIOS, pnp nvram, ACPI, etc.

The Bootstrap program will be loaded to 7c00h and then executed from 7c00h
B8000h is the first address of the VGA character mode video memory.
Because the address line in real mode is 20 bits, the maximum address range in real mode is 0-220-1, and 1 Mbit/s of address space can be accessed.
In protection mode, the address line is 32-bit. Therefore, the maximum address range in mode is 0-232-1. You can access 4G address space.