the Basic Input/Output System (BIOS) , also known as the System BIOS, is a boot firmware, designed to be the first code run by a PC when powered on. The initial function of the BIOS is to identify, test, and initialize system devices such as the video display card, hard disk, and floppy disk and other hardware. This is to prepare the machine into a known state, so that software stored on compatible media can be loaded, executed, and given control of the PC.
How It Works ?
The Operating System - An operating system(commonly abbreviated to either OS or O/S) is an interface between hardware and applications. The operating system acts as a host for the applications that are run on the machine. As a host, one of the purposes of an operating system is to handle the details of the operation of the hardware. windows 98, 2000, XP, Vista, Linux/Unix and Mac OS etc.
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.
What Actually 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 make sure that 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.
- Provides a low-level routines to operating system to interface all the hardware components.
- Managing a collection of settings for the Hard Disks, clock, etc.
Interrupt handlers are small pieces of software that act as translators between the hardware components and 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.
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.
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. 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.
While rebooting if you have left the Disk, you probably seen this message
This i the message you receive if a disk is in the drive
when you restart your computer.
Don't worry about it and it can be fix easily, just pop out the disk and press a key to continue.
Configuring BIOS
Now you know that the BIOS checks the CMOS Setup for custom settings. Here is the process to change those settings.
To enter the CMOS setup do the following :
- 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.
- 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
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.
Major BIOS manufacturers include:
- Americans Megatrends Inc. (AMI)
- Phoenix Technologies
- ALi
- Winbond
