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Nonvolatile BIOS memory refers to a small memory on PC motherboards that is used to store BIOS settings. It is traditionally called CMOS RAM because it uses a volatile, low-power complementary metal–oxide–semiconductor (CMOS) SRAM (such as the Motorola MC146818 [1] or similar) powered by a small battery when system and standby power is off. [2]
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.
However, BIOS manufacturers and OEMs have relied on SMM for newer functionality like Advanced Configuration and Power Interface (ACPI). [9] [10] Some uses of the System Management Mode are: Handle system events like memory or chipset errors; Manage system safety functions, such as shutdown on high CPU temperature; System Management BIOS (SMBIOS)
The BIOS also updates the ESCD each time the hardware configuration changes, after deciding how to re-allocate resources like IRQ and memory mapping ranges. After the ESCD has been updated, the decision need not be made again, which thereafter results in faster startup without conflicts until the next hardware configuration change.
After the POST completes and, in a BIOS that supports option ROMs, after the option ROM scan is completed and all detected ROM modules with valid checksums have been called, the BIOS calls interrupt 19h to start boot processing. Post-boot, programs loaded can also call interrupt 19h to reboot the system, but they must be careful to disable ...
INT 10h is fairly slow, so many programs bypass this BIOS routine and access the display hardware directly. Setting the video mode, which is done infrequently, can be accomplished by using the BIOS, while drawing graphics on the screen in a game needs to be done quickly, so direct access to video RAM is more appropriate than making a BIOS call ...
During the POST, the BIOS must integrate multiple competing, changing, and even mutually exclusive standards and initiatives for the matrix of hardware and operating systems the PC is expected to support, although at most only simple memory tests and the setup screen are displayed. The principal duties of the main BIOS during POST include:
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.