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The BIOS uses the boot devices set in Nonvolatile BIOS memory , or, in the earliest PCs, DIP switches. The BIOS checks each device in order to see if it is bootable by attempting to load the first sector (boot sector). If the sector cannot be read, the BIOS proceeds to the next device.
In computing, the System Management BIOS (SMBIOS) specification defines data structures (and access methods) that can be used to read management information produced by the BIOS of a computer. [1] This eliminates the need for the operating system to probe hardware directly to discover what devices are present in the computer.
BIOS-style booting from MBR-partitioned disks is commonly called BIOS-MBR, regardless of it being performed on UEFI or legacy BIOS-based systems. Furthermore, booting legacy BIOS-based systems from GPT disks is also possible, and such a boot scheme is commonly called BIOS-GPT.
An option ROM for the PC platform (i.e. the IBM PC and derived successor computer systems) is a piece of firmware that resides in ROM on an expansion card (or stored along with the main system BIOS), which gets executed to initialize the device and (optionally) add support for the device to the BIOS.
For modern simpler devices, such as USB keyboards, USB mouses and USB sound cards, the trend is to store the firmware in on-chip memory in the device's microcontroller, as opposed to storing it in a separate EEPROM chip. Examples of computer firmware include: The BIOS firmware used on PCs
Typical POST screen (AMI BIOS) Typical UEFI-compliant BIOS POST screen (Phoenix Technologies BIOS) Summary screen after POST and before booting an operating system (AMI BIOS) A power-on self-test ( POST ) is a process performed by firmware or software routines immediately after a computer or other digital electronic device is powered on.
The BIOS (Basic Input Output System) includes boot firmware and power management firmware. Newer motherboards use Unified Extensible Firmware Interface (UEFI) instead of BIOS. The CMOS (complementary MOS) battery, which powers the CMOS memory for date and time in the BIOS chip. This battery is generally a watch battery.
On IBM PC compatible machines, the BIOS is ignorant of the distinction between VBRs and MBRs, and of partitioning. The firmware simply loads and runs the first sector of the storage device. [3] If the device is a floppy or USB flash drive, that will be a VBR. If the device is a hard disk, that will be an MBR.