1.1 BIOS and UEFI – CompTIA A+ 220-901 Flashcards
What is the Basic Input/Output System?
The BIOS in modern PCs initializes and tests the system hardware components, and loads a boot loader or an operating system from a mass memory device. In the era of MS-DOS, the BIOS provided a hardware abstraction layer for the keyboard, display, and other input/output (I/O) devices that standardized an interface to application programs and the operating system. More recent operating systems do not use the BIOS after loading, instead accessing the hardware components directly.
What is POST?
A power-on self-test (POST) is a process performed by firmware or software routines immediately after a computer or other digital electronic device is powered on.
In the case of a computer, the POST routines are part of a device’s pre-boot sequence; if they complete successfully, the bootstrap loader code is invoked to load an operating system.
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
pass control to other specialized extension BIOSes (if installed)
identify, organize, and select which devices are available for booting
The functions above are served by the POST in all BIOS versions back to the very first. In later BIOS versions, POST will also:
discover, initialize, and catalog all system buses and devices
provide a user interface for system’s configuration
construct whatever system environment is required by the target operating system
Unified Extensible Firmware Interface (UEFI)
Can Support large >2.2TB GUID Partition Table
Unified Extensible Firmware Interface (UEFI)
Can Support large >2.2TB GUID Partition Table
Includes a pre-boot environment that can have a shell, drivers and applciations, browse the internet, backup storage devices, remote diagnostics.
CMOS (Memory)
Nowadays we use flash memory. Used to have to have a powersource but Flash doesn’t need it.
