BIOS (English basic input/output system «basic input output system») is part of the system software in the form of firmware that is required to provide the operating system API access to computer hardware and connected devices.
After we pressed the button to turn on the computer starts its work it is BIOS. Their mission is to determine how is the configuration of the components of your computer when you turn it on, as between themselves interact its components, as is the simplest input/output of data. BIOS determines the course of the process of booting the system, testing and configuration of the connected devices (Fig. 1, 2):
Testing of the processor;
Copy of the BIOS into memory and checking checksums BIOS;
Checking the memory regeneration and testing of 64 KB lower memory;
Search and configuring the video card (video card) - it was at this point on the screen appeared the first message;
Full testing of operative memory;
Test the keyboard and other input devices-output;
Check CMOS checksum and the status of the battery;
Initialization COM and LPT ports;
The distribution of system resources;
Initialization of the media from which you are downloading the computer's hard disk, USB drives, CD-ROM, booting from the network card on the technology PXE, etc.;
If booting from the first media failed, the BIOS tries the second on the list, and etc.
Because of the inertia of modern digital monitors see this picture, it is often impossible: it is disappearing faster than the monitor manages to complete the switch to the correct mode (Fig.3). But some video cards do not display any messages during its initialization. In some versions of the BIOS, you can disable any messages at boot - instead, it will display the manufacturer's logo.
After the end of testing, control is passed to the boot loader operating system. This boot loader is usually located in the Boot sector (the boot sector) of the hard disk and loads the OS (operating system) in the computer.
If as a result of all these manipulations something went wrong, the computer will signals with the help of the built-in speaker or on-screen error message will appear.
To open the BIOS need to press a key on the keyboard DEL, F2 or F10 (see Fig. 1, 2, 3).
If the same when you boot your computer displays only the manufacturer's logo, which covers all of the messages, then as soon as will be determined by the keyboard (flash indicator Num Lock, Caps Lock, Scroll Lock), several times in a row, press DEL.
After this will start the BIOS Setup program. Looks like the BIOS Setup like this:
Or is this:
This is a program with which you can change the settings in the BIOS.
Navigating the BIOS by using buttons «Up», «Down», «Right», «Left» (the button with the arrow on the keyboard), which moves the cursor (select partitions), and the key «Enter», «Esc» (select and deselect a selected section or paragraph, respectively).
After making changes all stored not in the BIOSе, in a special chip dynamic memory CMOS. In General in the BIOS to make changes is impossible without special hardware. These hardware, programmers, make the so-called «firmware upgrades». And for some older motherboards it is in principle impossible.
After turning on the computer in the course of testing of the equipment of the current configuration is compared with the one that is stored in CMOS memory. If there are differences, it happens automatically or update CMOS, or is caused by the BIOS Setup to change the settings.
In the BIOS chip all data is stored and when the computer is off. And that's CMOS memory requires power to ensure that all changes are saved and when a computer is disconnected from the electric power. Power supply is carried out using the rechargeable battery, which is located on the motherboard. The charge is usually enough for a few years.
If you want to reset all the settings for the BIOS Setup, then, to do this you need to pull out the battery for 10 minutes and all the contents of the CMOS is cleared.
When the loan period expires battery (battery sits), you may see a message «CMOS-checksum» or «Batteru Low Level». In this case, you just need to replace the battery with a new one and set the settings again, if they are introduced.