How BIOS works

1.Introduction to how BIOS works

One of the most common usesFlash MemoryIs forBasic Input/Output SystemOf your computer, commonly known as the BIOS (pronounced "Bye-ose "). on ally every computer available, the BIOS makes sure all the other chips, hard drives, ports and CPU function together.

EveryDesktopAndLaptopComputer in common use today containsMicroprocessorAs its central processing unit. The microprocessor isHardwareComponent. To get its work done, the microprocessor executes a set of instructions knownSoftware(SeeHow microprocessors workFor details). You are probably very familiar with two different types of software:

TheOperating System-Operating SystemProvides 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. (SeeHow operating systems workFor lots of details.)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,EmailApplication and so on. You can also buy new applications and install them.

Learn more BiOS quiz Computer Memory Curiosity project: can you compare computer processing to thinking?

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.

 

2. 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 thoseInstructions. 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,SCSIAnd 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 likeKeyboard,Screen, AndSerialAndParallel ports, Especially when the computer is booting.

Managing a collection of settings forHard Disks, Clock, etc.

BiOS uses flash memory, a type of Rom.

The BIOS is special software that interfaces The major hardware components of your computer withOperating System. It is usually stored onFlash MemoryCHIP ONMotherboard, But sometimes the chip is another typeRom.

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

Check the CMOS setup for custom settings load the interrupt handlers and device drivers initialize registers and power management perform the power-on self-test (post) display System settings determine which devices are bootable 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 participant 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 handlersAre 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. theDevice DriversAre 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, orShadowed,RamTo run faster

 

3. Booting the computer

Whenever you turn on your computer, the first thing you see is the BIOS software doing its thing. on each 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 isCold bootOrReboot. It does this by checking the value at memory address 0000: 0472. A value of 1234 h 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 using Ming a read/write test of each memory address. It checks the PS/2 ports orUSB portsFor a keyboard and a mouse. It looks forPeripheral 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 make y 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 typically provided des information about:

TheProcessorTheFloppy DriveAndHard driveMemoryBiOS revision and date display

This is the message you receive if a disk is in the drive when you restart your computer.

 

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 disk when you restarted your computer, you have probably seen this message.

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

4. Installing 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 duringInitial 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 dateBoot sequence-The order that BIOS will try to load the Operating SystemPlug and Play-A standard for auto-detecting connected devices; shocould be set to "yes" if your computer and operating system both support itMouse/keyboard-"Enable Num Lock," "enable the keyboard," "auto-detect mouse "...Drive configuration-Configure hard drives, CD-ROM and floppy drivesMemory-Direct the BIOS to shadow to a specific memory addressSecurity-Set a password for accessing the computerPower Management-Select whether to use power management, as well as set the amount of timeStandbyAndSuspendExit-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 shoshould choose "Save changes" and exit. the BIOS will then restart your computer so that the new settings take effect.

The BIOS usesCMOSTechnology to save any changes made to the computer's settings. With this technology, a small lithium or Ni-CADBatteryCan 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!

 

5. 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 BIOSBiOS upgrades.

Major BIOS Manufacturers include:

American megatrends Inc. (AMI)Phoenix TechnologiesAliWINBOND

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 cocould upgrade 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.

For more information on bios and related topics, check out the links on the next page.

6. Lots more information

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More great links

Webopedia: BIOS

PC guide: system BIOS

Kingston's ultimate memory Guide

A Brief History of microprogramming

Wim's BIOS

American megatrends (AMI)

Phoenix Technologies

Ali

WINBOND

 

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