Another function of the BIOS setup program is to customize specific aspects of the computer hardware to fit individual needs. The features that can be customized are determined by the BIOS manufacturer and version. Before making changes to the BIOS, it is important to have a clear understanding of how the changes can affect the computer. Incorrect settings can have an adverse effect.

Time and Date

The main page of the BIOS has a System Time field and a System Date field to set the system clock, as shown in Figure 1. It is important to set these fields to the correct time and date because they are referenced by the operating system and other programs. If the date and time are not set properly, a maintenance program might think that it is out of date and constantly try to update files, or a calendar program will not display reminders on the correct date or time.

Disabling Devices

You can configure advanced BIOS settings to disable devices that are not needed or not used by the computer, as shown in Figure 2. For instance, a motherboard might have built-in video, sound, or network capabilities and installing a dedicated adapter card for one or more of these capabilities renders the built-in device redundant. Instead of wasting resources on the built-in device, you can disable the feature in the BIOS.

You can also disable extra hard drive controllers, serial ports, FireWire ports, or infrared hardware. If a device is not working, check the advanced BIOS settings to see if the device is disabled by default or has been disabled by someone. Enable the device in the BIOS so that it can be used by the computer.

Boot Order

An ordered list of devices that a computer is allowed to boot from is called the boot order or boot sequence. This list is typically located in the BIOS under the Boot tab, as shown in Figure 3. You can designate hard drives, optical drives, floppy drives, network boot, and flash media in the boot order. To allow USB booting, enable this option in the BIOS.

Shortly after completing POST, the computer attempts to load the operating system. The BIOS checks the first device in the boot order for a bootable partition. If the device has no bootable partition, the computer checks the next device in the list. When a device with a bootable partition is found, the BIOS checks for an installed operating system.

The order in which devices are listed in the boot order depends on user needs. For example, when installing an operating system, an optical drive, network boot, or USB drive might need to be listed before a bootable hard drive. It is recommended to reorder the list after installing all operating systems to boot first from a bootable hard drive. The BIOS also allows you to disable or remove devices from the boot order list.

Clock Speed

Some BIOS setup programs allow you to change the CPU clock speed, as shown in Figure 4. Reducing the CPU clock speed makes the computer run slower and cooler. This might result in less noise from fans and can be useful if a quieter computer is desired, such as in a home theater or bedroom.

Increasing the CPU clock speed makes the computer run faster but also hotter, possibly causing the computer to be louder due to increased fan speeds. Increasing the CPU clock speed beyond the manufacturer recommendations is known as overclocking. Overclocking a CPU is risky and voids the warranty of the CPU. Overclocking can result in a shorter life span or cause damage to the CPU if the clock speed is increased too much. It is a common practice to install a cooling system capable of dissipating the extra heat created by overclocking so that the CPU is not damaged.


Virtualization technology allows a computer to run multiple operating systems in separate files or partitions. To accomplish this, a computer virtualization program emulates the characteristics of an entire computer system, including the hardware, BIOS, operating system, and programs. Enable the virtualization setting in the BIOS for a computer that will be using virtualization technology, as shown in Figure 5. Disable this setting if virtualization does not perform correctly or will not be used.