2.5. Basic input / output system (BIOS). CMOS RAM concept

The Basic Input Output System (BIOS) is, on the one hand, an integral part of the hardware, and on the other, one of the OS software modules. The emergence of this name is due to the fact that the BIOS includes a set of input-output programs. With these programs, OS and application programs can interact with various devices of the computer itself, as well as with peripheral devices.

As an integral part of the hardware, the BIOS system in the PC is implemented as a single chip installed on the computer's motherboard. Most modern video adapters and storage controllers have their own BIOS, which complements the system BIOS. One of the BIOS developers is IBM, which created NetBIOS. This software product cannot be copied, so other computer manufacturers were forced to use BIOS chips from independent companies. Specific BIOS versions are related to the chipset (or chipset) located on the motherboard.

As an OS program module, the BIOS system contains a test program when the computer is turned on POST (Power On Self Test - self-test when the computer is turned on). When you run this program, the basic components of the computer (processor, memory, etc.) are tested. If there are problems with powering the computer, that is, the BIOS cannot perform the initial test, then the error notification will look like a sequence of beeps.

Information about the computer's configuration (amount of memory, types of drives, etc.) is stored in the “unchangeable” CMOS RAM memory. This is the information that the BIOS software modules need. This memory is made on the basis of a certain type of CMOS structures (CMOS - Complementary Metal Oxide Semiconductor), which are characterized by low power consumption. CMOS memory is non-volatile, as it is powered by a battery located on the system board, or a battery of galvanic cells mounted on the case of the system unit.

Changing the settings in CMOS is done through the SETUP program. It can be called up by pressing a special key combination (DEL, ESC, CTRL-ESC, or CRTL-ALT-ESC) during boot-up (some BIOSes allow you to run SETUP at any time by pressing CTRL-ALT-ESC). In AMI BIOS, this is most often done by pressing the DEL key (and holding it) after pressing the RESET button or turning on the computer.

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