e820 is shorthand for the facility by which the

BIOS In computing, BIOS (, ; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is a type of firmware used to provide runtime services for operating systems and programs and to perform hardware initialization d ...

of an

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 8086 microprocessor and its 8-bit-external-bus variant, the 8088. Th ...

-based computer system 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" has different meanings in different contexts. #It is the fastest and most flexible cach ...

to the

operating system An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ...

boot loader A bootloader, also spelled as boot loader or called bootstrap loader, is a computer program that is responsible for booting a computer and booting an operating system. If it also provides an interactive menu with multiple boot choices then it's o ...

. It is accessed via the int 15h

call Call or Calls may refer to: Arts, entertainment, and media Games * Call (poker), a bet matching an opponent's * Call, in the game of contract bridge, a bid, pass, double, or redouble in the bidding stage Music and dance * Call (band), from L ...

, 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 The Linux kernel is a Free and open-source software, free and open source Unix-like kernel (operating system), kernel that is used in many computer systems worldwide. The kernel was created by Linus Torvalds in 1991 and was soon adopted as the k ...

, 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. Booting When initially booted, a computer system load ...

command.

References

External links

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