What is BIOS | What is CMOS | What is UEFI BIOS

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What is BIOS:​

BIOS is stands for Basic Input Output System. basically BIOS is for checking the systems's hardware details and its functions at startup, BIOS is non volatile memory chip that store the hardware details that is attached to the machine/ computer, if there is no power on the machine or no 3.3v button battery present on the motherboard, BIOS programs and settings will be intact. Where as CMOS

What is CMOS:​

CMOS stands for Complementary Metal Oxide Semiconductor. in the BIOS chip all the information about the computer hardware details stored from the manufacturer point. after the machine comes to the end user, that end user will make changes to the machine default functions, such as first boot drive, boot orders, boot menu keys etc.. so when end user changes the default function to the machines, that changes stored on the CMOS chip, CMOS chip is a volatile memory, the changes will not be retained once no power to the machine, on order to keep the changes in memory the system needs power, for this purpose only the 3.3v Button cell is there on all the motherboards, that voltage keeps the machine to maintain that changes and runs the time and date of the machine.

What is EUFI:

UEFI Stands for Unified Extensible Firmware Interface. UEFI is a software/firmware that connects between computer hardware and Operating System, UEFI replaces the legacy Basic Input/Output System (BIOS) firmware interface. most UEFI firmware implementations providing support for legacy BIOS services. UEFI can support remote diagnostics and repair of computers, even with no operating system installed. EUFI supports more sized hard disk drive


In addition to the standard PC disk partition scheme that uses a master boot record (MBR), UEFI also works with the GUID Partition Table (GPT) partitioning scheme, which is free from many of the limitations of MBR. In particular, the MBR limits on the number and size of disk partitions (up to four primary partitions per disk, and up to 2 TB.

UEFI Boot Process​

want to know more details : en.wikipedia.org