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System Configuration

For the BIOS to be able to start the computer, you've seen that it must find an operating system on a hard disk or floppy disk drive. But how does the BIOS know where the drives are located or what types they are?

Floppy disk drives and hard disk drives are two of the most important items that must be configured in the BIOS. If the drive types are not correctly identified in the BIOS, the BIOS will not be able to start the system. Whenever you build a system or change major components, you need to run the BIOS setup program to check or change settings.

Starting the Setup Program

On most systems built since the late 1980s, the BIOS configuration program is stored in the BIOS chip itself. On a few current systems, as with the original IBM AT, the setup program must be run from a floppy disk drive or the hard drive. The original IBM PC and PC/XT had only a few settings, and these were made by manipulating a series of small rocker or slide switches called DIP switches.

ROM-based setup programs are normally started by pressing one or more keys in combination within the first few seconds after turning on the computer. Although these keystrokes vary from system to system, the most popular keys on current systems include the escape (Esc) key, the Delete key, the F1 key, and various combinations of Ctrl+Alt+ another specified key. Most computers display the correct key(s) to press during the initial startup screen. Check with your system vendor for the appropriate keystrokes or to see if you need to run a program from MS-DOS or Windows to configure your system.

Because the settings you make in the BIOS setup program are stored in the nonvolatile RAM of the CMOS chip, the settings are often called CMOS settings.

In the following section, we will review the typical setup process, looking at each screen of a typical Pentium-class system.

Step-by-Step CMOS/BIOS Configuration

The A+ Certification exam will test your knowledge of basic CMOS/BIOS configuration. To help you prepare for the exam, this section covers the most important portions of the CMOS/BIOS setup process.

To start the CMOS setup process, press the correct key(s) during the bootstrap process or run the setup program from hard disk or floppy disk after the computer has started. On virtually all systems built since the early 1990s, you'll start with a menu screen, as shown in Figure 3.6. This menu, as well as the contents of the screens listed, will vary according to your BIOS brand, version, and motherboard type.

Figure 3.6
Select the menu item from this CMOS Setup menu to examine or change settings.

Select Standard CMOS Setup to begin.

Other systems will immediately display the Standard CMOS Setup screen, which is typically used to configure drive, date, and time settings.

Standard CMOS Configuration

The standard CMOS configuration screen (see Figure 3.7) includes settings for items such as

  • Date

  • Time

  • Floppy disk drive types for drives A: (first floppy disk drive) and B: (second floppy disk drive)

  • Hard drives connected to the IDE interface

Figure 3.7
A typical standard setup screen. On this system, hard drives can be detected during the boot process ("Auto" setting), but they can also be user-defined, as shown here.

To make selections here, you normally press keys to cycle through the different options, including date and time.

The time must be entered in the 24-hour format (1:00PM = 13:00, and so on). Enable daylight savings unless your state or area (Arizona, Hawaii, and parts of Indiana) doesn't switch to DST in the spring and summer.

Change the default floppy drive types to match your current configuration if necessary. See "Floppy Disk Drives," page 191, for details on selecting the correct floppy disk drive type.

To select the correct hard drive type, you can use one of three methods:

  • Manually enter the correct settings.

  • Use an auto-detection feature located here or from the main menu.

  • Allow the system to detect the hard drives during every system boot.

Some systems also display the amount of memory onboard on this screen, but only extremely old systems based on 386 or older processors require that you manually enter the amount of RAM in the system. On virtually all systems using a 286 processor or better, the standard CMOS configuration screens are extremely similar, varying mainly in the number and types of drives that can be used.

The standard setup screen is the single most important screen in the entire BIOS/CMOS setup process. If the drives are not defined correctly, the system cannot boot.

Automatic Configuration of BIOS/CMOS Settings

Many versions of the AMI and Award BIOS allow you to automatically configure all screens except the Standard setup screen with a choice of these options from the main menu:

  • BIOS Defaults (also referred to as Original/Fail-Safe on some systems)

  • Setup Defaults (also referred to as Optimal on some systems)

  • Turbo

Use BIOS defaults to troubleshoot the system because these settings are very conservative in memory timings and other options. Normally, the Setup defaults provide better performance. Turbo, if present, speeds up the memory refresh rate used by the system. As you view the setup screens in this chapter, you'll note these options are listed. If you use either automatic setup after you make manual changes, all your manual changes will be overridden!

Appropriately, the graphical AMI WinBIOS uses a tortoise, a hare, and an eagle for these three options.

With many recent systems, you can select Optimal or Setup Defaults, save your changes, and exit, and the system will work acceptably. However, you might want more control over your system. In that case, look at the following screens and make the changes necessary.

Advanced CMOS Configuration

The advanced CMOS configuration screen, shown in Figure 3.8, allows you to adjust optional details about the computer. In this screen, you can adjust the NumLock setting, type of video, keyboard repeats speed, settings for cache memory, and other special features. Most systems built since the early 1990s include this screen.

Figure 3.8
A typical Advanced CMOS Configuration screen, also known as the BIOS Features screen—use this screen to enable or disable anti-virus hardware features, adjust boot sequence, and adjust memory options such as cache and parity checking.

Table 3.1 lists the most important options and my recommendations.

Table 3.1  Recommended Advanced CMOS Settings




Write-Protect Boot Sector, Virus Warning, or Antivirus Protection

Enable for normal system use

This doesn't really stop viruses, but it will help prevent users from accidentally FORMATting or FDISKing the hard disk.

Cache Internal


Cache memory makes system faster (see and External"Adding Main and Cache RAM," page 54.

Boot Sequence

C: (first hard disk), A: (floppy disk drive), CD-ROM, C:, A:

Prevents users from booting with floppy floppy disk left in A: won't spread disks; boot sector viruses to the system; system won't stop if floppy disk is left in A:.


Enable for memory addresses containing firmware (BIOS) chips

Copies firmware contents such as system BIOS, video BIOS, and add-on card BIOS to RAM. Located between 640KB-1MB (upper memory blocks).

LBA mode

See "Overcoming Hard Disk Capacity Limitations with LBA Mode," page 211


Depending on the system, you might be able to boot from CD-ROM, ZIP, or LS-120 drives in addition to the floppy disk drives and hard drives traditionally available as boot devices, as shown in Figure 3.9.

Depending on the BIOS version, you might need to press the ESC key, as in Figure 3.9, to return to the main menu, or use cursor keys to move directly to another menu screen.

Figure 3.9
This recent Pentium-class system offers a variety of boot options. To view the settings for any CMOS configuration option, either use the help key (F1) as shown here, or press the correct key to step through the options for the setting.

Advanced Chipset/Chipset Features Configuration

The Advanced Chipset/Chipset Features Configuration screen, like the one shown in Figure 3.10, offers many advanced options that vary by the system. The following are some typical features of this menu:

  • Memory types, speed and timing—Adjust the values here to match the memory installed in the system (such as parity, non-parity, SDRAM, EDO, and so on).

  • Cache adjustments—Some Cyrix CPUs require the user to disable pipelining for proper operation.

  • Configuration of USB ports—If you upgrade a system to Windows 98 or Windows 2000, you might need to enable the USB ports; systems with older versions of Windows (which didn't support USB) might not have the USB ports enabled. The USB Keyboard Support feature must be enabled if a USB keyboard is installed to allow the keyboard to operate outside of Windows.

  • Configuration of the AGP slot—Depending on the specific AGP video card installed (if any), you might need to set the size of the memory aperture used to transfer data between the system and the AGP port and select the AGP mode (1x, 2x, and 4x).

Figure 3.10
This recent system's USB (Universal Serial Bus) and AGP (Advanced Graphics Port) options are located on the Chipset Features configuration screen, along with the usual system and memory-timing options.

Power Management Configuration

Virtually all systems built since the mid-1990s are designed to allow power management; watch for the EPA "Energy Star" logo when you start the computer.

Power management works like this: After a user-defined period of inactivity, devices such as the monitor, the hard drive, or even the CPU will go into different low-power modes:

  • Standby mode—Shuts off the hard drive and blanks monitor screens that use Display Power Management Signaling. Move the mouse or press a key to "wake up" the system.

  • Suspend mode—Turns off the CPU clock to save even more power. Systems that fully support suspend mode allow you to choose a special shutdown option that "remembers" what programs and files were open, and can bring the system back to that state when the power is restored.

Early power-management systems require that you, the user, keep working with the mouse or keyboard to prevent the system from going into power-saving modes, which can cause modem or network transfers to be interrupted, losing data.

On most newer systems, such as the one featured in Figure 3.11, you can prevent the system from going into power-saving modes, or to wake up when activity takes place, by setting these options by either the device name (modem, hard drive, floppy disk drive, parallel port, serial port) or by the device's IRQ (see "IRQs, DMAs, I/O Port Addresses, and Memory Addresses," page 17.

I have always regarded power management as being a great idea that does not always work well in practice.

Figure 3.11
This recent system has support for both ACPI power management (used by Windows 98) and APM (used by earlier versions of Windows).

To make power management work, you need to make sure that

  • Devices such as hard drives and monitors can be powered down and powered back up without loss of information.

  • Power management is set to monitor network and Internet devices, such as modems and network cards, for activity to prevent the connection from being dropped.

  • All devices installed in a system are monitored for activity to prevent data loss. For example, Figure 3.11 does not list IRQ 15 (used by the secondary IDE host adapter in most systems) as a PM (power management) event. Activity on IRQ 15 will not wake up the system, although the computer could be reading data from devices on IRQ 15 or saving data to devices on IRQ 15.

  • Users understand how power management works.

Normal signs of power management in use include

  • Monitors with blinking power lights, or power lights a different color than normal, while the screen remains blank

  • Keyboards that seem "dead" for a few seconds after you start typing (because the hard drive must spin up)

Users who are unfamiliar with power management might panic and reboot the computers (losing their data!) or demand that you "fix" their systems. Sometimes, the best fix is to disable power management completely or to use Windows to configure power management settings through its Power icon in Control Panel. For systems that have ACPI- compatible BIOS chips that also run Windows 98 or Windows 2000, Windows should be used to manage power.

Adjust the system to the user's requirements, and continue.

PnP (Plug-and-Play) Configuration Screen

Plug-and-Play (PnP) configuration allows either the operating system or the system BIOS to select hardware settings for PnP-compatible cards when first installed and to change those settings when new cards are installed. PnP BIOS support has been part of virtually all systems shipped with Windows 95 or newer versions of Windows, and virtually all add-on cards and other devices (such as printers, monitors, modems, and so on) also support PnP configuration.

Early versions of the Plug-and-Play Configuration screen (see Figure 3.12) were introduced with the first Pentium-based systems with PCI slots, because PCI cards could configure themselves. PnP can be used with PnP-compatible ISA cards as well as with PCI and AGP cards. If you are using Windows 95, 98, or 2000, set Plug and Play Operating System to Yes. Unless you have problems with installing cards, that is normally all you need to set. If you are having problems adding cards, you can set IRQs to be available to PnP devices (add-on cards that are set by Windows) or to ISA/Legacy devices (ports built into the motherboard or ISA cards you must set manually).

Some systems, as in this example, also allow you to enable or disable IRQ use for USB, VGA video, and ACPI power management. You can disable IRQ usage for any or all of these devices, but some devices might not work if no IRQ is assigned.

Built-In Ports/Peripherals Setup

You can enable or disable most ports built into recent systems with the Built-in Ports/Peripherals Setup screen, shown in Figure 3.13. (Some systems with PS/2 mouse ports require that you adjust a jumper block on the motherboard.) On some systems, this screen also lets you adjust advanced hard disk options, such as PIO mode and block mode.

Figure 3.12
A typical Plug-and-Play configuration screen. By changing PnP options for IRQs and DMA channels to Legacy, you can reserve selected IRQs and DMAs for non-PnP cards.

Figure 3.13
This system's COM 2 port (UART 2) is disabled to allow an internal modem to be installed as COM 2.

Generally, you disable a built-in port if you add a card containing a port that will conflict with it. For example, you can disable COM 2 (serial port 2) to allow you to install an internal modem. You can also adjust the IRQ and I/O port addresses used by the built-in parallel and serial ports. On some systems, the LBA mode setting for hard disks and USB configuration options are also found on this screen. After observing or changing the settings, return to the main menu and continue.

See "IDE Performance Optimization," page 212, for information about hard disk options PIO mode and block mode.


You can enable two types of passwords on many systems: a power-on password that must be entered to allow any use of the system, and a setup password that must be entered to allow access to the BIOS/CMOS setup. If you don't have all the settings recorded (with screen printouts or by writing them down), this can be dangerous to enable.

Why? If the passwords are lost, users are locked out of the system, and you would need to remove the battery or use the "clear CMOS" jumper on the motherboard to erase the CMOS record of the passwords—and all other settings. This would require reconfiguring the system BIOS from scratch!

Because passwords are useful to prevent tampering with system settings, record the system information first, before you enable this feature.

Saving and Recording BIOS/CMOS Settings

Most BIOSes allow you to save your changes, or discard changes you might have made accidentally, when you exit the main menu and restart the system.

A few old BIOSes automatically save any changes, even bad ones. In either case, be sure to review the standard CMOS setup screen and any others you viewed to make sure the settings are acceptable before you save and exit. You should record critical BIOS settings, such as drive type information and any other changes from a system's default settings. Many technicians find it useful to add a sticker with drive type and other information to the rear of a system or to the inside of the system cover.

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