BIOS

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File Format
Name BIOS
Ontology
Extension(s) .bin, .rom

BIOS (Basic Input Output System), is a ROM chip containing code (firmware) to control peripherals attached to a wikipedia:PC.

The x86 BIOS entry point is located at physical address 0xfffffff0 (usually corresponding to 16 bytes from the end of the BIOS image) and is executed in 16-bit real mode; it usually contains a jump instruction (either far or near). There are no other guarantees about BIOS image layout, although many vendors have developed in-house formats.

UEFI firmware images usually contain an embedded Firmware File System.

Identification

ROM images start with bytes 0xaa 0x55. At offset 2 the initialization vector is stored. In many cases this is a 3 byte jump instruction starting with hexadecimal value 0xE9. Images for cards with PCI interface contain a 4 byte signature PCIR. Images for cards which support plug and Play feature contain a 4 byte signature $PnP.

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