e820

{{Short description|Memory map information provided by x86-based BIOS}}

{{Lowercase title}}

File:BIOS e820 example screenshot.png

e820 is shorthand for the facility by which the BIOS of an x86-based computer system reports the memory map to the operating system or boot loader.{{cite web

| url=https://uefi.org/sites/default/files/resources/ACPI_4_Errata_A.pdf

| title=Advanced Configuration and Power Interface Specification

| date=2010-04-05

| publisher=Unified Extensible Firmware Interface Forum

| access-date=2020-03-11}}

It is accessed via the int 15h call, by setting the {{mono|AX}} register to value E820 in hexadecimal.

It reports which memory address ranges are usable and which are reserved for use by the BIOS.{{cite web

| url=http://www.uruk.org/orig-grub/mem64mb.html

| title=INT 15h, AX=E820h - Query System Address Map

| author=Erich Boleyn

| date=1996-07-02

| access-date=2020-03-11}}

BIOS-e820 is often the first thing reported by a booting Linux kernel, and it can also be seen with the dmesg command.