# E820

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> Markdown URL: https://mediated.wiki/source/E820.md
> Source: https://en.wikipedia.org/wiki/E820
> Source revision: 1229740140
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{{Short description|Memory map information provided by x86-based BIOS}}
{{Lowercase title}}
upright=1.2|thumb|Example of e820 information from dmesg
'''e820''' is shorthand for the facility by which the [BIOS](/source/BIOS) of an [x86](/source/x86)-based computer system reports the [memory map](/source/memory_map) to the [operating system](/source/operating_system) or [boot loader](/source/boot_loader).<ref>{{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](/source/Unified_Extensible_Firmware_Interface) Forum
| access-date=2020-03-11}}</ref>

It is accessed via the [int](/source/INT_(x86_instruction)) 15h [call](/source/BIOS_interrupt_call), by setting the {{mono|AX}} register to value <code>E820</code> in hexadecimal.
It reports which memory address ranges are usable and which are reserved for use by the BIOS.<ref>{{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}}</ref>

BIOS-e820 is often the first thing reported by a booting [Linux kernel](/source/Linux_kernel), and it can also be seen with the [dmesg](/source/dmesg) command.

==References==
<references/>

==External links==
* [https://wiki.osdev.org/Detecting_Memory_(x86)#BIOS_Function:_INT_0x15.2C_EAX_.3D_0xE820 Detecting Memory (x86): BIOS Function: INT 0x15, EAX = 0xE820]

Category:BIOS

{{Comp-hardware-stub}}

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Adapted from the Wikipedia article [E820](https://en.wikipedia.org/wiki/E820) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/E820?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.