Friday, July 20, 2007

BIOS basics and advanced learning

Main Menu
The standard CMOS Setup menu dates back to the 286 days, when the complete BIOS Setup consisted
of only one menu. In the standard menu, you can set the system clock and record hard disk and
floppy drive parameters and the basic video type. Newer BIOSes have more complicated setups with
more menus and submenus, so the main menu often is fairly sparse compared to older systems.
The main menu in a modern system reports system information such as the BIOS version, the processor
type and speed, the amount of memory, and whether the memory or cache is configured for ECC
functionality. The main menu also can be used to set the system date and time.


Typical Main Menu Settings*




BIOS Version

No options

Displays the version of the BIOS

Processor Type

No options

Displays the processor type

Processor Speed

No options

Displays the processor speed

System Bus

No options

Displays the system bus frequency


Cache RAM

No options

Displays the size of second-level (L2) cache and whether it is ECC capable

Total Memory

No options

Displays the total amount of RAM on the motherboard

Memory Bank 0

No options

Displays size and type of DIMM installed in each memory

Memory Bank 1


Memory Bank 2


English (default) Deutch

Selects the default language used by the BIOS


Processor Serial

Disabled (default),

Enables/disables processor serial number (present only when



a Pentium III CPU is installed)

System Time

Hour, minute, second

Specifies the current time

System Date

Month, day, year

Specifies the current date


Typical Advanced Menu Settings*




Extended Configuration

No options

If Used is displayed, User-defined has been selected in the Extended Configuration under the Maintenance menu.

PCI Configuration

No options

Configures the IRQ priority of individual PCI slots. When selected, displays the PCI Configuration submenu.

Boot Settings Configuration

No options

Configures Numlock and Plug and Play, and resets configura-tion data. When selected, displays the Boot Configuration sub-


Peripheral Configuration

No options

Configures peripheral ports and devices. When selected, displays the Peripheral Configuration submenu.

IDE Configuration

No options

Specifies type of connected IDE device.

Diskette Configuration

No options

When selected, displays the Diskette Configuration submenu.

Event Log

No options

Configures Event Logging. When selected, displays the Event Log Configuration submenu.

Video Configuration

No options

Configures video features. When selected, displays the Video Configuration submenu.


Additional Advanced Menu Settings*




Plug and Play O/S

No (default),

Specifies whether a Plug and Play operating system is being


used. No—lets the BIOS configure all devices. Yes—lets the operating system configure Plug and Play devices. Not required with a Plug and Play operating system.

Reset Configuration Data

No (default),

Clears the Plug and Play BIOS configuration data on the next




Auto (default),

Specifies the power-on state of the Num Lock feature on the

On, Off

numeric keypad of the keyboard.

Resource Configuration

No options

Configures memory blocks and IRQs for legacy ISA devices.

When selected, displays the Resource Configuration submenu.


Additional Advanced Features Settings



Auto Configuration*

Selects predetermined optimal values of chipset parameters. When Disabled, chipset parameters revert to setup information stored in CMOS. Many fields in this screen are not available when Auto Configuration is Enabled.

EDO DRAM Speed Selection

The value in this field must correspond to the speed of the EDO DRAM installed in your system. This value is access speed, so a lower value means a faster



This field lets you control the number of cycles between a row activate com-mand and a read or write command.

SDRAM RAS Precharge Time*

The precharge time is the number of cycles it takes for the RAS to accumulate its charge before DRAM refresh. If insufficient time is allowed, refresh might be incomplete, and the DRAM might fail to retain data.

SDRAM CAS Latency Time*

When synchronous DRAM is installed, you can control the number of cycles between when the SDRAMs sample a read command and when the controller samples read data from the SDRAMs.

SDRAM Precharge Control

When Enabled, all CPU cycles to SDRAM result in an All Banks Precharge command on the SDRAM interface.

DRAM Data Integrity Mode

Select Non-ECC or ECC (error correcting code) according to the type of installed DRAM. ECC allows for single-bit error correction and multibit error detection at a slight speed penalty to the system.

System BIOS Cacheable

Allows caching of the system BIOS ROM at F0000h–FFFFFh, resulting in better system performance. If any program writes to this memory area, a system error can result.

Video BIOS Cacheable

Allows caching of the video BIOS ROM at C0000h–C7FFFh, resulting in better video performance. If any program writes to this memory area, a system error can result.

Video RAM Cacheable*

Selecting Enabled allows caching of the video memory (RAM) at

(Video Memory Cache Mode)

A0000h–AFFFFh, resulting in better video performance. If any program writes to this memory area, a memory access error can result. Uncacheable Speculative Write-Combining (USWC) mode is the same as Enabled on some


8/16 Bit I/O Recovery Time

The I/O recovery mechanism adds bus clock cycles between PCI-originated I/O cycles to the ISA bus. This delay takes place because the PCI bus is so much faster than the ISA bus.

Memory Hole at 15M–16M

Places a 1MB empty RAM area between 15MB and 16MB. Older software sometimes would not run with 16MB or more memory in the system; enabling this provides a workaround. This is normally not used.

Passive Release

When Enabled, CPU-to-PCI bus accesses are allowed during passive release. Otherwise, the arbiter accepts only another PCI master access to local DRAM.

Delayed Transaction

The chipset has an embedded 32-bit posted write buffer to support delay transactions cycles. Select Enabled to support compliance with PCI specification version 2.1.

AGP Aperture Size (MB)

Select the size of the accelerated graphics port (AGP) aperture. The aperture is a portion of the PCI memory address range dedicated for graphics memory address space. Host cycles that hit the aperture range are forwarded to the AGP without any translation.

CPU Warning Temperature

Select the combination of lower and upper limits for the CPU temperature if

your computer contains an environmental monitoring system. If the CPU

temperature extends beyond either limit, any warning mechanism programmed

into your system is activated.

Current CPU Temperature

This field displays the current CPU temperature if your computer contains an

environmental monitoring system.

Shutdown Temperature

Select the combination of lower and upper limits for the system shutdown

temperature if your computer contains an environmental monitoring system. If

the temperature extends beyond either limit, the system shuts down.

CPUFAN Turn On IN Win98

If you are running Windows 98, which supports ACPI, selecting Enabled gives

the user a cooling choice at runtime. The user can run with the CPU fan turned

on or off, depending on deciding factors such as CPU activity, battery power

consumption, and noise tolerance.

Current System Temperature

This field displays the current system temperature if your computer contains a

monitoring system.

Current CPUFAN 1/2/3 Speed

These fields display the current speed of up to three CPU fans if your computer

contains a monitoring system.


These fields display the current voltage of up to seven voltage input lines if your

computer contains a monitoring system.

Spread Spectrum

When the system clock generator pulses, the extreme values of the pulse gener-

ate excess EMI. Enabling pulse spectrum spread modulation changes the

extreme values from spikes to flat curves, thus reducing EMI. This benefit in

some cases might be outweighed by problems with timing-critical devices, such

as a clock-sensitive SCSI device.

Legacy USB support means support for USB keyboards and mice. If you are using USB keyboards and
mice, you will find that the keyboard is not functional until a USB-aware operating system is loaded.
This can be a problem when running DOS, diagnostics software, or other applications that run outside
of USB-aware operating systems, such as Windows 98, Windows Me, Windows XP, and Windows
2000. In that case, you should enable the USB legacy support via this menu.
Even with legacy support disabled, the system still recognizes a USB keyboard and enables it to work
during the POST and BIOS Setup. With USB legacy support in the default (disabled) mode, the system
operates as follows:
1. When you power up the computer, USB legacy support is disabled.
2. POST begins.
3. USB legacy support is temporarily enabled by the BIOS. This enables you to use a USB keyboard
to enter the setup program or the Maintenance mode.
4. POST completes and disables USB legacy support (unless it was set to Enabled while in Setup).
5. The operating system loads. While the operating system is loading, USB keyboards and mice are
not recognized. After the operating system loads the USB drivers, the USB devices are recognized.
To install an operating system that supports USB, enable USB legacy support in BIOS Setup and follow
the operating system's installation instructions. After the operating system is installed and the USB
drivers are configured, USB legacy support is no longer used, and the operating system USB drivers
take over. However, I recommend that you leave legacy support enabled so the USB keyboard functions
in DOS while running self-booting or DOS-based diagnostics, or when running other
non–USB-aware operating systems.
Note that if USB legacy support is enabled, you shouldn't mix USB and PS/2 port keyboards and mice.
For example, don't use a PS/2 keyboard with a USB mouse or a USB keyboard and a PS/2 mouse. Also
remember that this legacy support is for keyboards and mice only; it won't work for USB hubs or
other USB devices. For devices other than keyboards or mice to work, you need a USB-aware operating
system with the appropriate USB drivers.

Security Menu
Most BIOSes include two passwords for security, called the supervisor and user passwords. These passwords
help control who is allowed to access the BIOS Setup program and who is allowed to boot the
computer. The supervisor password is also called a setup password because it controls access to the
setup program. The user password is also called a system password because it controls access to the
entire system.
If a supervisor password is set, a password prompt is displayed when an attempt is made to enter the
BIOS Setup menus. When entered correctly, the supervisor password gives unrestricted access to view
and change all the Setup options in the Setup program. If the supervisor password is not entered or is
entered incorrectly, access to view and change Setup options in the Setup program is restricted.
If the user password is set, the password prompt is displayed before the computer boots up. The password
must be entered correctly before the system is allowed to boot. Note that if only the supervisor
password is set, the computer boots without asking for a password because the supervisor password
controls access only to the BIOS Setup menus. If both passwords are set, the password prompt is displayed
at boot time, and either the user or the supervisor password can be entered to boot the computer.
In most systems, the password can be up to seven or eight characters long.
If you forget the password, most systems have a jumper on the board that allows all passwords to be
cleared. This means that for most systems, the password security also requires that the system case be
locked to prevent users from opening the cover and accessing the password-clear jumper. This jumper
is often not labeled on the board for security reasons, but it can be found in the motherboard or system
Provided you know the password and can get into the BIOS Setup, a password can also be cleared by
entering the BIOS Setup and selecting the Clear Password function. If no Clear function is available,
you can still clear the password by selecting the Set Password function and pressing Enter (for no
password) at the prompts.

Table 5.26

Typical Security Settings*




User Password Is

No options.

Reports whether a user password is set.


No options.

Reports whether a supervisor password is set.

Password Is

Set User

Password can be up to seven

Specifies the user password.


alphanumeric characters.

Set Supervisor

Password can be up to seven

Specifies the supervisor password.


alphanumeric characters.

Clear User

No options.

Clears the user password.


User Setup


Controls the user's capability to run the BIOS Setup


View Only Limited Access


Full Access (default).

Unattended Start

Disabled (default)

Enables the unattended start feature. When enabled,


the computer boots, but the keyboard is locked. The user

must enter a password to unlock the computer or boot

from a disk.

*Based on the BIOS used by the Intel DB815EEA motherboard. Used by permission of Intel Corporation.


Plug and Play BIOS
Traditionally, installing and configuring devices in PCs has been a difficult process. During installation,
the user is faced with the task of configuring the new card by selecting the IRQ, I/O ports, and
DMA channel. In the past, users were required to move jumpers or set switches on the add-in cards to
control these settings. They needed to know exactly which resources were already in use so they could
find a set of resources that did not conflict with the devices already in the system. If a conflict exists,
the system might not boot and the device might fail or cause the conflicting hardware to fail.
PnP is technology designed to prevent configuration problems and provide users with the capability
to easily expand a PC. With PnP, the user simply plugs in the new card and the system configures it
automatically for proper operation.
PnP is composed of three principal components:
 Plug and Play BIOS
 Extended System Configuration Data (ESCD)
 Plug and Play operating system
The PnP BIOS initiates the configuration of the PnP cards during the boot-up process. If the cards previously
were installed, the BIOS reads the information from ESCD and initializes the cards and boots
the system. During the installation of new PnP cards, the BIOS consults the ESCD to determine which
system resources are available and needed for the add-in card. If the BIOS is capable of finding sufficient
available resources, it configures the card. However, if the BIOS is incapable of locating sufficient
available resources, the Plug and Play routines in the operating system complete the configuration
process. During the configuration process, the configuration registers (in flash BIOS) on the card and
the ESCD are updated with the new configuration data.
PnP Device IDs
All Plug and Play devices must contain a Plug and Play device ID to enable the operating system to
uniquely recognize the device so it can load the appropriate driver software. Each device manufacturer
is responsible for assigning the Plug and Play ID for each product and storing it in the hardware.
Each manufacturer of Plug and Play devices must be assigned an industry-unique, three-character vendor
ID. Then, the device manufacturer is responsible for assigning a unique product ID to each individual
product model. After an ID is assigned to a product model, it must not be assigned to any
other product model manufactured by the same company (that is, one that uses the same vendor ID).
BIOS Error Messages
When a PC system is first powered on, the system runs a POST. If errors are encountered during the
POST, you usually see a text error message displayed onscreen. Errors that occur very early in the
POST might happen before the video card is initialized. These types of errors can't be displayed, so the
system uses two other alternatives for communicating the error message. One is beeping—the system
beeps the speaker in a specific pattern that indicates which error has occurred.
The other alternative is to send a hexadecimal error code to I/O port address 80h, which can be read
by a special card in one of the bus slots. When the ROM BIOS is performing the POST, in most systems
the results of these tests are continuously sent to I/O Port 80h so they can be monitored by special
diagnostics cards called POST cards (see Figure 5.7). These tests sometimes are called manufacturing
tests because they were designed into the system for testing systems on the assembly line without a
video display attached.
The POST cards have a two-digit hexadecimal display used to report the number of the currently executing
test routine. Before executing each test, a hexadecimal numeric code is sent to the port, and
then the test is run. If the test fails and locks up the machine, the hexadecimal code of the last test
being executed remains on the card's display.
Many tests are executed in a system before the video display card is enabled, especially if the display
is EGA or VGA. Therefore, many errors can occur that would lock up the system before the system
could possibly display an error code through the video system. Because not all these errors generate
beep codes, to most normal troubleshooting procedures, a system with this type of problem (such as a
memory failure in Bank 0) would appear completely "dead." By using one of the commercially available
POST cards, however, you can often diagnose the problem.
These codes are completely BIOS dependent because the card does nothing but display the codes sent
to it. Some BIOSes have more detailed POST procedures and therefore send more informative codes.
POST cards can be purchased from JDR Microdevices or other sources and are available in both ISA
and PCI bus versions.
For simple but otherwise fatal errors that can't be displayed onscreen, most of the BIOS versions also
send audio codes that can be used to help diagnose such problems. The audio codes are similar to
POST codes, but they are read by listening to the speaker beep rather than by using a special card.

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