e820 is shorthand for the facility by which the BIOS of

x86 x86 (also known as 80x86 or the 8086 family) is a family of complex instruction set computer (CISC) instruction set architectures initially developed by Intel based on the Intel 8086 microprocessor and its 8088 variant. The 8086 was intr ...

-based computer systems reports the

memory map In computer science, a memory map is a structure of data (which usually resides in memory itself) that indicates how memory is laid out. The term "memory map" can have different meanings in different contexts. *It is the fastest and most flexible ...

to the

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also i ...

boot loader A bootloader, also spelled as boot loader or called boot manager and bootstrap loader, is a computer program that is responsible for booting a computer. When a computer is turned off, its softwareincluding operating systems, application code, a ...

. It is accessed via the int 15h

call Call or Calls may refer to: Arts, entertainment, and media Games * Call, a type of betting in poker * Call, in the game of contract bridge, a bid, pass, double, or redouble in the bidding stage Music and dance * Call (band), from Lahore, Paki ...

, by setting the register to value E820 in hexadecimal. It reports which memory address ranges are usable and which are reserved for use by the BIOS. BIOS-e820 is often the first thing reported by a booting Linux kernel, and it can also be seen with the

dmesg dmesg (''diagnostic messages'') is a command on most Unix-like operating systems that prints the message buffer of the kernel. The output includes messages produced by the device drivers. Command On many Unix-like systems, the boot process g ...

command.

References

External links

Detecting Memory (x86): BIOS Function: INT 0x15, EAX = 0xE820
BIOS {{Comp-hardware-stub