E820

Short description: Memory map information provided by x86-based BIOS

Example of e820 information from dmesg

e820 is shorthand for the facility by which the BIOS of x86-based computer systems reports the memory map to the operating system or boot loader.[1]

It is accessed via the int 15h call, by setting the AX register to value `E820` in hexadecimal. It reports which memory address ranges are usable and which are reserved for use by the BIOS.[2]

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

## References

1. ↑ "Advanced Configuration and Power Interface Specification". Unified Extensible Firmware Interface Forum. 2010-04-05. https://uefi.org/sites/default/files/resources/ACPI_4_Errata_A.pdf.
2. ↑ Erich Boleyn (1996-07-02). "INT 15h, AX=E820h - Query System Address Map". http://www.uruk.org/orig-grub/mem64mb.html.

## External links

* Detecting Memory (x86): BIOS Function: INT 0x15, EAX = 0xE820

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