The interaction between the computer hardware and the user is carried out using the operating system - Mac OS, Linux, Windows. The intermediary between the operating system and the computer components is the BIOS, the basic input / output system that starts immediately after turning on the computer.
What is BIOS
BIOS is a collection of firmware that controls all of the components on a motherboard. Once loaded into RAM, the BIOS runs the computer's Power On Self Test (POST). The test checks the power management system, RAM, peripheral ports, hard drives and their controllers, initializes system resources and chipset registers.
System configuration data is stored in a dedicated CMOS (Complementary Metal Oxide Semiconductor) memory chip. This microcircuit has its own power source - a round battery located on the motherboard.
After 3-5 years of operation, the battery runs out. This causes the CMOS content to be cleared and an error message is displayed when the computer is turned on.
During the test, the BIOS compares information about the current state of the computer and that contained in the CMOS. If differences are found, the program either updates the contents of the memory chip or prompts the user to make changes in the Setup BIOS.
The BIOS reports the results of the check with a set of beeps. One short signal indicates the successful completion of the test, after which control of the computer is transferred to the operating system. The BIOS searches for the OS loader program in the sequence indicated in the Boot Record section (different manufacturers may call it differently): hard drive, flash drive, CD or DVD drive. The priority of boot devices is user-defined.
If a critical hardware malfunction has been detected, a combination of short and long beeps is emitted. Their decoding is provided by the BIOS developer in the manual for the motherboard and on the official website. Sometimes the error message is displayed in text form on the monitor.
To enter the Setup BIOS, you must press the F2, F10 or Delete key, depending on the BIOS developer. A prompt line indicating the required key appears on the screen after the POST beep.
What is ROM
BIOS commands are written in read-only memory (ROM) - non-volatile flash memory. Usually the ROM case is marked with a bright holographic sticker, so the BIOS chip is easy to find. It is located in a special block on the motherboard, from where it can be removed if necessary. In this case, care must be taken not to bend the contacts of the microcircuit.
Modern EEPROMs can be flashed, i.e. change their content. There are special programs for flashing the BIOS. The need for this procedure arises, in particular, if the old motherboard conflicts with new hardware, for example, a large hard disk.
