BIOS (Basic Input/Output System) and UEFI (Unified Extensible Firmware Interface) are types of firmware stored on a computer’s motherboard that start the computer and prepare it to run the operating system.

When you turn on a computer, BIOS or UEFI:

1. Performs a hardware check (called POST – Power-On Self Test)
2. Initializes hardware like CPU, RAM, keyboard, and storage devices
3. Loads the operating system from the hard drive into memory

BIOS

• The traditional and older firmware system
• Works in a basic text mode
• Has limited features and supports smaller disk sizes

UEFI

• The modern replacement for BIOS
• Faster and more powerful
• Supports large hard drives and modern hardware
• Provides a graphical interface and better security features (like Secure Boot)

Conclusion:

BIOS and UEFI are essential startup programs that initialize hardware and load the operating system, with UEFI being the advanced and modern version of BIOS.