BIOS
BIOS - Basic Input Output System. Това е компютърна програма, работеща на най-ниско ниво (позната е още и като firmware), която се стартира първа при включването на компютъра.
Предназначение
Основната функция на тази програма е да инициализира стандартния хардуер (клавиатура, графичен адаптер, памет, USB и мрежови и др. контролери) и да зареди необходимите драйвери за управлението му.
BIOS software is stored on a non-volatile ROM chip on the motherboard. It is specifically designed to work with each particular model of computer, interfacing with various devices that make up the complementary chipset of the system. In modern computer systems, the BIOS contents is stored on an EEPROM chip so that the contents can be rewritten without removing it from the motherboard. This allows BIOS software to be easily upgraded to add new features or fix bugs.
A BIOS has a user interface (UI), typically a menu system accessed by pressing a certain key on the keyboard when the PC starts. In the BIOS UI, a user can: configure hardware set the system clock enable or disable system components select which devices are eligible to be a potential boot device set various password prompts, such as a password for securing access to the BIOS user interface functions itself and preventing malicious users from booting the system from unauthorized peripheral devices.
POST
Първата задача на BIOS е да стартира POST (Power On Self Test). POST includes routines to set an initial value for internal and output signals and to execute internal tests, as determined by the device manufacturer
POST protects the bootstrapped code from being interrupted by faulty hardware.
The BIOS begins its POST when the CPU is reset. The first memory location the CPU tries to execute is known as the reset vector. In the case of a hard reboot, the northbridge will direct this code fetch (request) to the BIOS located on the system flash memory. For a warm boot, the BIOS will be located in the proper place in RAM and the northbridge will direct the reset vector call to the RAM.
During the POST flow of a contemporary BIOS, one of the first things a BIOS should do is determine the reason it is executing. For a cold boot, for example, it may need to execute all of its functionality. If, however, the system supports power saving or quick boot methods, the BIOS may be able to circumvent the standard POST device discovery, and simply program the devices from a preloaded system device table.
The principal duties of the main BIOS during POST are as follows: verify CPU registers verify the integrity of the BIOS code itself verify some basic components like DMA, timer, interrupt controller find, size, and verify system main memory initialize BIOS discover, initialize, and catalog all system buses and devices pass control to other specialized BIOSes (if and when required) provide a user interface for system's configuration identify, organize, and select which devices are available for booting construct whatever system environment that is required by the target operating syste
