BIOS
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| − | '''BIOS''' (Basic Input Output System), is a [[Read Only Memory|ROM]] chip containing code (firmware) to control peripherals attached to a [[ | + | '''BIOS''' (Basic Input Output System), is a [[Read Only Memory|ROM]] chip containing code (firmware) to control peripherals attached to a [[Wikipedia:PC|PC]]. |
The x86 BIOS entry point is located at physical address <code>0xfffffff0</code> (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. | The x86 BIOS entry point is located at physical address <code>0xfffffff0</code> (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. | ||
Revision as of 07:14, 2 August 2025
BIOS (Basic Input Output System), is a ROM chip containing code (firmware) to control peripherals attached to a 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 3 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.
Sample files
- http://minuszerodegrees.net/rom/rom.htm - many older ROM images without Plug and Play.
- https://www.xtideuniversalbios.org/ - BIOS for IDE ATA hard disks.
- http://rayer.g6.cz/romos/romose.htm -
romos.binfor loading FreeDOS. - https://www.qemu.org/ - Download QEMU and extract or install → *.bin - ROM examples for cards with PCI interface.
