The final step in the configuration of a new computer, BIOS setup, allows the customization of a computer to function optimally based on the hardware and software profiles. The BIOS code is typically embedded in ROM or a read-only memory chip on the motherboard, which is discussed in Chapter 2 "How Computers Work". The ROM chip is read-only, meaning it cannot be changed normally. This protects the ROM from disk, RAM, or power failures that could corrupt it. Additionally, it ensures that the BIOS code is always available since it is a requirement for the system to boot. Although the BIOS cannot be changed while loaded in memory, the basic BIOS program can be updated. Newer BIOS ROM chips are of a type called Electrically Erasable Programmable Read-Only Memory (EEPROM), also called flash BIOS. Flash BIOS allows the upgrade of the BIOS software from a disk provided by the manufacturer without replacing the chip. BIOS upgrades are typically used by manufacturers to fix flaws in the BIOS code, called bugs, and improve system capabilities.

Evolution of the BIOS
The basic design standard of the system BIOS was originally developed by the IBM Corporation for use in its XT and AT computer systems in the early 1980s. Unfortunately, the IBM BIOS only worked with IBM hardware. Therefore, other manufacturers who built "clones" of these systems had to guarantee compatibility of the computers with the IBM standard. Cloning was necessary in order to guarantee that the computer software applications developed for IBM systems would run on their systems as well. By the late 1980s, a few companies had successfully developed compatible BIOS that other manufacturers could use. Three companies have since come to dominate the BIOS market:

• Phoenix Technologies, Ltd. (Phoenix)
• American Megatrends, Inc. (AMI)
• Award Software, Inc. (Award)

Of these three, Phoenix now concentrates primarily in the specialized laptop computer market, while AMI and Award are the chief suppliers to the modern non-IBM computer market. Note that Award is now a division of Phoenix Technologies.

BIOS Function
The BIOS function is not complex. It initially runs basic device test programs and then seeks to configure these devices. The system BIOS and the information required to configure it are stored on a Complementary Metal-Oxide Semiconductor (CMOS) chip. CMOS is a battery-powered storage chip located on the system board. The CMOS chip has rewritable memory since the configuration data can be changed or updated as the components or devices in the computer are changed. The point is that the CMOS allows the BIOS upgrade.

Configuration of the BIOS on a computer is called the BIOS setup. It is also called the CMOS setup, named for the chip that stores the BIOS settings. It is especially important to get the BIOS setup right the first time. Since the BIOS scans the system at boot time and compares what it finds against settings in CMOS, it must be properly configured in order to avoid errors. Proper operation of the system depends on the BIOS loading the correct program code for its devices and internal components. Without the correct code and device drivers, the system will either not boot properly or work inconsistently with frequent errors.

If a system crashes or fails unexpectedly, it can be restarted thanks to the BIOS. Built into the BIOS is a comprehensive self-diagnostic routine called the Power-On Self-Test (POST), which checks the internal system circuits at boot-up and gives error codes. POST is discussed more thoroughly in Chapter 2. After the initial circuit checks, the BIOS also checks the internal components against a known list of operating devices stored in the CMOS chip. Any problems are indicated using error codes or messages. These error messages will help in diagnosing and repairing the problem. In order for the BIOS to have meaningful diagnostics and error checking, the internal components and devices of a newly assembled computer need to be configured properly in CMOS.

Worksheet  (PDF, 7 KB)   What is BIOS?