Bios basic input output system optimization common terms explained
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Bios basic input output system optimization common terms explained



How BIOS Works 6

What BIOS Does 6

Booting the Computer 8

Configuring BIOS 9

Updating Your BIOS 10

Bootstrap Management 11

Boot Other Device 11

Boot Sequence 11

Boot Sequence EXT Means 12

Boot To OS/2 12

Boot Up Floppy Seek 12

Boot Up NumLock Status 13

Delay IDE Initial 13

First Boot Device 14

Init Display First 14

Primary Graphics Adapter 15

Primary VGA BIOS 15

Quick Boot 16

Quick Power On Self Test 16

Report No FDD For Win95 17

Reset Configuration Data 17

Resource Controlled By 18

Second Boot Device 18

Third Boot Device 19

Graphics Subsystem 19

AGP 2X Mode 19

AGP 4X Drive Strength 20

AGP 4X Mode 20

AGP 8X Mode 20

AGP Always Compensate 21

AGP Aperture Size 21

AGP Clock / CPU FSB Clock 22

AGP Drive Strength 22

AGP Drive Strength N Ctrl 23

AGP Drive Strength P Ctrl 23

AGP Driving Control 24

AGP Driving Value 24

AGP Fast Write 25

AGP ISA Aliasing 25

AGP Master 1WS Read 25

AGP Master 1WS Write 26

AGP Prefetch 26

AGP Secondary Lat Timer 26

AGP Spread Spectrum 27

AGP to DRAM Prefetch 28


DBI Output for AGP Trans. 28

Graphic Win Size 29

No Mask of SBA FE 30

PCI/VGA Palette Snoop 30

Post Write Combine 31

USWC Write Posting 31

Video BIOS Cacheable 32

Video BIOS Shadowing 33

Video Memory Cache Mode 34

Video RAM Cacheable 34

Memory Subsystem 35

Act Bank A to B CMD Delay 35

Delay DRAM Read Latch 36

DRAM Act to PreChrg CMD 37

DRAM Data Integrity Mode 37

DRAM Idle Timer 38

DRAM Interleave Time 38

DRAM PreChrg to Act CMD 39

DRAM Ratio (CPU:DRAM) 39

DRAM Ratio H/W Strap 40

DRAM Read Latch Delay 41

DRAM Refresh Rate 42

Fast R-W Turn Around 42

Force 4-Way Interleave 42

Gate A20 Option 43

MD Driving Strength 44

Memory Hole At 15M-16M 44

OS Select For DRAM > 64MB 45

OS/2 Onboard Memory > 64M 45

Read-Around-Write 46

Read Wait State 46

Refresh Interval 47

Refresh Mode Select 47

SDRAM 1T Command 48

SDRAM 1T Command Control 48

SDRAM Bank Interleave 49

SDRAM Burst Len 50

SDRAM Burst Length 50

SDRAM CAS Latency Time 50

SDRAM Command Rate 51

SDRAM Cycle Length 51

SDRAM Cycle Time Tras/Trc 52

SDRAM Idle Limit 52

SDRAM RAS Precharge Time 53

SDRAM RAS Pulse Width 53

SDRAM RAS-to-CAS Delay 54

SDRAM Row Active Time 54

SDRAM Tras Timing Value 55

SDRAM Trp Timing Value 55

Super Bypass Mode 56

Super Bypass Wait State 56

SuperStability Mode 57

Miscellaneous 58

Anti-Virus Protection 58

Duplex Select 58

Flash BIOS Protection 59

Floppy 3 Mode Support 59

Hardware Reset Protect 59

KBC Input Clock Select 60

Onboard IR Function 60

Onboard Parallel Port 60

Onboard Serial Port 1 61

Onboard Serial Port 2 61

Onboard USB Controller 62

Parallel Port Mode 62

Power On Function 63

RxD, TxD Active 63

Security Setup 64

Spread Spectrum 64

USB Controller 65

Virus Warning 65

Processor 66

Athlon 4 SSED Instruction 66

Auto Turn Off PCI Clock Pin 66

Clock Throttle 67

Compatible FPU OPCODE 67

CPU Drive Strength 68

CPU Fast String 68

CPU Hyper-Threading 68

CPU L2 Cache ECC Checking 69

CPU Level 1 Cache 69

CPU Level 2 Cache 70

CPU Level 3 Cache 70

CPU Thermal-Throttling 71

CPU VCore Voltage 71

Delay Prior To Thermal 72

FPU OPCODE Compatible Mode 73

Host Bus In-Order Queue Depth 73

Hyper-Threading Technology 74

In-Order Queue Depth 74


K7 CLK_CTL Select 76

L3 Cache 77

Level 2 Cache Latency 77

N/B Strap CPU As 78

Processor Number Feature 79

S2K Bus Driving Strength 79

S2K Strobe N Control 80

S2K Strobe P Control 80

Speed Error Hold 81

Storage Subsystem 81

32-bit Disk Access 81

32-bit Transfer Mode 82

ATA100RAID IDE Controller 82

HDD S.M.A.R.T. Capability 82

IDE Bus Master Support 83

IDE HDD Block Mode 84

Master Drive PIO Mode 84

Master Drive UltraDMA 85

Onboard FDD Controller 86

Onboard IDE-1 Controller 86

Onboard IDE-2 Controller 87

PCI IDE Busmaster 87

Swap Floppy Drive 88

System Bus 88

16-bit I/O Recovery Time 88

8-bit I/O Recovery Time 89

AT Bus Clock 89

Auto Detect DIMM/PCI Clk 90

Byte Merge 90

CPU to PCI Post Write 90

CPU to PCI Write Buffer 91

Delayed Transaction 91

Disable Unused PCI Clock 92

FSB Spread Spectrum 92

ISA 14.318MHz Clock 93

ISA Enable Bit 93

Master Priority Rotation 94

P2C/C2P Concurrency 94

Passive Release 95

PCI 2.1 Compliance 95

PCI Chaining 96

PCI Clock / CPU FSB Clock 97

PCI Delay Transaction 98

PCI Dynamic Bursting 99

PCI IRQ Activated By 99

PCI Latency Timer 100

PCI Master 0 WS Read 100

PCI Master 0 WS Write 101

PCI Master Read Caching 101

PCI Pipelining 101

PCI Prefetch 102

PCI Target Latency 102

PCI to DRAM Prefetch 103

PCI#2 Access #1 Retry 103

Split Lock Operations 104

Synchronouse Mode Select 104

VLink 8X Support 104

System Resource Management 105

APIC Function 105

Assign IRQ For USB 105

Assign IRQ For VGA 106

ECP Mode Use DMA 106

EPP Mode Select 106

Force Update ESCD 107

Interrupt Mode 107

MPS Control Version For OS 108

MPS Revision 108

PIRQ x Use IRQ No. 109

PNP OS Installed 109


How BIOS Works

One of the most common uses of Flash memory is for the basic input/output system of your computer, commonly known as the BIOS (pronounced „bye-ose“). On virtually every computer available, the BIOS makes sure all the other chips, hard drives, ports and CPU function together.

Every desktop and laptop computer in common use today contains a microprocessor as its central processing unit. The microprocessor is the hardware component. To get its work done, the
microprocessor executes a set of instructions known as software (see How Microprocessors Work for details). You are probably very familiar with two different types of software:

• The operating system – The operating system provides a set of services for the applications running on your computer, and it also provides the fundamental user interface for your computer. Windows 98 and Linux are examples of operating systems. (See How Operating Systems Work for lots of details.)

• The applications – Applications are pieces of software that are programmed to perform specific tasks. On your computer right now you probably have a browser application, a word processing application, an e-mail application and so on. You can also buy new applications and install them.

It turns out that the BIOS is the third type of software your computer needs to operate successfully. In this article, you’ll learn all about BIOS — what it does, how to configure it and what to do if your BIOS needs updating.

What BIOS Does

The BIOS software has a number of different roles, but its most important role is to load the operating system. When you turn on your computer and the microprocessor tries to execute its first instruction, it has to get that instruction from somewhere. It cannot get it from the operating system because the operating system is located on a hard disk, and the microprocessor cannot get to it without some instructions that tell it how. The BIOS provides those instructions. Some of the other common tasks that the BIOS performs include:

• A power-on self-test (POST) for all of the different hardware components in the system to make sure everything is working properly

• Activating other BIOS chips on different cards installed in the computer – For example, SCSI and graphics cards often have their own BIOS chips.

• Providing a set of low-level routines that the operating system uses to interface to different hardware devices – It is these routines that give the BIOS its name. They manage things like the keyboard, the screen, and the serial and parallel ports, especially when the computer is booting.

• Managing a collection of settings for the hard disks, clock, etc.

The BIOS is special software that interfaces the major hardware components of your computer with the operating system. It is usually stored on a Flash memory chip on the motherboard, but sometimes the chip is another type of ROM. BIOS uses Flash memory, a type of ROM.

When you turn on your computer, the BIOS does several things. This is its usual sequence:

1. Check the CMOS Setup for custom settings

2. Load the interrupt handlers and device drivers

3. Initialize registers and power management

4. Perform the power-on self-test (POST)

5. Display system settings

6. Determine which devices are bootable

7. Initiate the bootstrap sequence

The first thing the BIOS does is check the information stored in a tiny (64 bytes) amount of RAM located on a complementary metal oxide semiconductor (CMOS) chip. The CMOS Setup provides detailed information particular to your system and can be altered as your system changes. The BIOS uses this information to modify or supplement its default programming as needed. We will talk more about these settings later.

Interrupt handlers are small pieces of software that act as translators between the hardware components and the operating system. For example, when you press a key on your keyboard, the signal is sent to the keyboard interrupt handler, which tells the CPU what it is and passes it on to the operating system. The device drivers are other pieces of software that identify the base hardware components such as keyboard, mouse, hard drive and floppy drive. Since the BIOS is constantly intercepting signals to and from the hardware, it is usually copied, or shadowed, into RAM to run faster.

Booting the Computer

Whenever you turn on your computer, the first thing you see is the BIOS software doing its thing. On many machines, the BIOS displays text describing things like the amount of memory installed in your computer, the type of hard disk and so on. It turns out that, during this boot sequence, the BIOS is doing a remarkable amount of work to get your computer ready to run. This section briefly describes some of those activities for a typical PC.

After checking the CMOS Setup and loading the interrupt handlers, the BIOS determines whether the video card is operational. Most video cards have a miniature BIOS of their own that initializes the memory and graphics processor on the card. If they do not, there is usually video driver information on another ROM on the motherboard that the BIOS can load.

Next, the BIOS checks to see if this is a cold boot or a reboot. It does this by checking the value at memory address 0000:0472. A value of 1234h indicates a reboot, and the BIOS skips the rest of POST. Anything else is considered a cold boot.

If it is a cold boot, the BIOS verifies RAM by performing a read/write test of each memory address. It checks the PS/2 ports or USB ports for a keyboard and a mouse. It looks for a peripheral component interconnect (PCI) bus and, if it finds one, checks all the PCI cards. If the BIOS finds any errors during the POST, it will notify you by a series of beeps or a text message displayed on the screen. An error at this point is almost always a hardware problem.

The BIOS then displays some details about your system. This
includes information about:

• The processor

• The floppy drive and hard drive

• Memory

• BIOS revision and date

• Display

Any special drivers, such as the ones for small computer system interface (SCSI) adapters, are loaded from the adapter, and the BIOS displays the information. The BIOS then looks at the sequence of storage devices identified as boot devices in the CMOS Setup. „Boot“ is short for „bootstrap,“ as in the old phrase, „Lift yourself up by your bootstraps.“ Boot refers to the process of launching the operating system. The BIOS will try to initiate the boot sequence from the first device. If the BIOS does not find a device, it will try the next device in the list. If it does not find the proper files on a device, the startup process will halt. If you have ever left a floppy disk in the drive when you restarted your computer, you have probably seen this message. This is the message you get if a floppy disk is in the drive when you restart your computer.

The BIOS has tried to boot the computer off of the floppy disk left in the drive. Since it did not find the correct system files, it could not continue. Of course, this is an easy fix. Simply pop out the disk and press a key to continue.

Configuring BIOS

In the previous list, you saw that the BIOS checks the CMOS Setup for custom settings. Here’s what you do to change those settings.

To enter the CMOS Setup, you must press a certain key or combination of keys during the initial startup sequence. Most systems use „Esc,“ „Del,“ „F1,“ „F2,“ „Ctrl-Esc“ or „Ctrl-Alt-Esc“ to enter setup. There is usually a line of text at the bottom of the display that tells you „Press ___ to Enter Setup.“

Once you have entered setup, you will see a set of text screens with a number of options. Some of these are standard, while others vary according to the BIOS manufacturer. Common options include:

• System Time/Date – Set the system time and date

• Boot Sequence – The order that BIOS will try to load the operating system

• Plug and Play – A standard for auto-detecting connected devices; should be set to „Yes“ if your computer and operating system both support it

• Mouse/Keyboard – „Enable Num Lock,“ „Enable the Keyboard,“ „Auto-Detect Mouse“…

• Drive Configuration – Configure hard drives, CD-ROM and floppy drives

• Memory – Direct the BIOS to shadow to a specific memory address

• Security – Set a password for accessing the computer

• Power Management – Select whether to use power management, as well as set the amount of time for standby and suspend

• Exit – Save your changes, discard your changes or restore default settings CMOS Setup

Be very careful when making changes to setup. Incorrect settings may keep your computer from booting. When you are finished with your changes, you should choose „Save Changes“ and exit. The BIOS will then restart your computer so that the new settings take effect.

The BIOS uses CMOS technology to save any changes made to the computer’s settings. With this technology, a small lithium or Ni-Cad battery can supply enough power to keep the data for years. In fact, some of the newer chips have a 10-year, tiny lithium battery built right into the CMOS chip!

Updating Your BIOS

Occasionally, a computer will need to have its BIOS updated. This is especially true of older machines. As new devices and standards arise, the BIOS needs to change in order to understand the new hardware. Since the BIOS is stored in some form of ROM, changing it is a bit harder than upgrading most other types of software.

To change the BIOS itself, you’ll probably need a special program from the computer or BIOS manufacturer. Look at the BIOS revision and date information displayed on system startup or check with your computer manufacturer to find out what type of BIOS you have. Then go to the BIOS manufacturer’s Web site to see if an upgrade is available. Download the upgrade and the utility program needed to install it. Sometimes the utility and update are combined in a single file to download. Copy the program, along with the BIOS update, onto a floppy disk. Restart your computer with the floppy disk in the drive, and the program erases the old BIOS and writes the new one. You can find a BIOS Wizard that will check your BIOS at BIOS Upgrades.

Major BIOS manufacturers include:

• American Megatrends Inc. (AMI)

• Phoenix Technologies

• ALi

• Winbond

As with changes to the CMOS Setup, be careful when upgrading your BIOS. Make sure you are upgrading to a version that is compatible with your computer system. Otherwise, you could corrupt the BIOS, which means you won’t be able to boot your computer. If in doubt, check with your computer manufacturer to be sure you need to upgrade.

Bootstrap Management

Boot Other Device

Common Options : Enabled, Disabled

Quick Review

This BIOS feature determines whether the BIOS will attempt to load an operating system from the Second Boot Device or Third Boot Device if it fails to load one from the First Boot Device.

This feature is enabled by default and it is recommended that you leave it as such.

Boot Sequence

Common Options : A, C, SCSI




D, A, SCSI (only when you have at least 2 IDE hard disks)

SCSI (only when you have at least 3 IDE hard disks)

F, A, SCSI (only when you have 4 IDE hard disks)





Quick Review

This BIOS feature enables you to set the sequence by which the BIOS will search for an operating system during the boot-up process. To ensure the shortest booting time possible, set the hard disk that contains your operating system as the first choice. Normally, this would be drive C for IDE drives but if you are using a SCSI hard disk, then select SCSI.

Some motherboards have an external (not part of the chipset) IDE controller. In such motherboards, the SCSI option is replaced with an EXT option. If you want to boot from an IDE hard disk running off the internal IDE controller, do not set the Boot Sequence to start with EXT. Please note that this feature works in conjunction with the Boot Sequence EXT Means feature.

Boot Sequence EXT Means

Common Options : IDE, SCSI

Quick Review

This BIOS feature determines whether the system boots from an IDE hard disk connected to an external IDE controller or a SCSI hard disk. However, it will only have an effect if the EXT option had been selected in the Boot Sequence feature.

To boot from an IDE hard disk that’s connected to the external IDE controller, you must set this feature to IDE.

In order to boot from a SCSI hard disk, you must set this feature to SCSI.

Boot To OS/2

Common Options : Yes, No

Quick Review

This is similar to the OS Select For DRAM > 64M BIOS feature.

This BIOS feature determines how systems with more than 64MB of memory are managed. A wrong setting can cause problems like erroneous memory detection.

If you are using an older version of the IBM OS/2 operating system, you should select Yes.

If you are using the IBM OS/2 Warp v3.0 or higher operating system, you should select No.

If you are using an older version of the IBM OS/2 operating system but have already installed all the relevant IBM FixPaks, you should select No.

Users of non-OS/2 operating systems (like Microsoft Windows XP) should select the No option.

Boot Up Floppy Seek

Common Options : Enabled, Disabled

Quick Review

This BIOS feature determines whether the BIOS checks for a floppy drive during boot-up or not.

If enabled, the BIOS will attempt to detect and initialize the floppy drive. If it cannot detect one, it will flash an error message. However, the system will still be allowed to continue the boot process.

If this feature is disabled, the BIOS will skip the floppy drive check. This speeds up the booting process by several seconds.

Since a floppy drive check is really pointless, it is recommended that you disable this feature for a faster booting process.

Boot Up NumLock Status

Common Options : On, Off

Quick Review

This BIOS feature sets the input mode of the numeric keypad at boot up.

If you turn this feature on, the BIOS will set the numeric keypad to function in the numeric mode.

If you set it to Off, the numeric keypad will function in the cursor control mode instead.

The numeric keypad’s input mode can be switched to either numeric or cursor control mode and back again at any time after boot up.

The choice of initial keypad input mode is entirely up to your preference.

Delay IDE Initial

Common Options : 0 to 15

Quick Review

Motherboards are capable of booting up much faster these days. Therefore, initialization of IDE devices now take place much earlier. Unfortunately, this also means that some older IDE drives will not be able to spin up in time to be initialized! When this happens, the BIOS will not be able to detect that IDE drive and the drive will not be accessible even though it is actually running just fine.

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