When you turn on a computer its RAM is empty. In order for it to be able to do something at all it needs a program. By design a CPU of a IBM PC compatible always looks in the same place for this, namely a fixed address near the top of the 1 megabyte real-mode address space. Here it finds BIOS (Basic Input/Output System), the first program run in the computer. In the case of a cold start the first order of business is a full scale test, identification and initialization of all system components. All available RAM is tested and tallied up, interrupt and DMA controllers initialized as well as the rest of the chipset, video display card, keyboard, hard disk drive, optical disc drive and other basic hardware. BIOS then locates the boot loader software and gives it control of the PC.
The changing role of BIOS
Older operating systems, such as MS-DOS, rely heavily on BIOS to communicate with the hardware of the PC. BIOS services, however, are not used by modern multitasking GUI operating systems after they initially load. Newer operating systems, like Windows NT, use their own native drivers; this makes it much easier to extend support to new hardware.
Later BIOS took on more complex functions by way of interfaces such as ACPI; these functions include power management, hot swapping, and thermal management.
As of 2011, the BIOS is being replaced by the more complex Extensible Firmware Interface (EFI) in many new machines. EFI is a specification which replaces the runtime interface of the legacy BIOS. The distinction between BIOS and EFI, however, is rarely made in terminology by the average computer user, making BIOS a catch-all term for both systems.
2012 Exam Objectives
You will be expected to be familiar with:
- Flashing the BIOS
- Accessing component information about RAM, CPU, hard and optical drives
- Configuring security options such as BIOS password and drive encryption
- Configuring boot sequence, enabling and disabling devices, date/time, clock speeds and virtualization support
- Monitoring temperature, fan speeds, intrusion detection/notification, voltage, clock and bus speeds
- Using built in diagnostic tools
Flashing the BIOS
In modern PCs the BIOS is stored in rewritable memory, allowing the contents to be replaced or 'rewritten.' Rewriting the contents is sometimes called flashing. This can be done by a special program usually provided by the system's manufacturer, or at the Power On Self Test, using a BIOS image from a hard drive or USB flash drive. A file containing such contents is sometimes called a 'BIOS image.' A BIOS might be reflashed in order to upgrade to a newer version to fix bugs or provide improved performance or to support newer hardware, or reflashing might be needed to fix a damaged BIOS.