A bootloader is a small program that manages the boot process of a computer system. It acts as an interface between the hardware and the software of a computer system. In simpler words, it is a software component that loads the operating system into the memory of the computer.

Bootloaders are present on all computing devices, including laptops, desktops, smartphones, and tablets. They decide which software to run at startup and how it should be loaded. A bootloader is responsible for initializing the hardware devices, running self-tests, and loading the operating system.

The boot process starts with the power being turned on or the reset button being pressed. The first piece of code that executes in the system is the BIOS, which is stored in a non-volatile memory chip on the motherboard. The BIOS performs a power-on self-test (POST) to check the integrity of the hardware and loads the bootloader from the boot device.

Once the bootloader is loaded, it starts the process of loading the operating system. The bootloader looks for the operating system files on the boot device and loads the files into the memory. It then hands over the control to the operating system.

Bootloaders are typically coded in low-level languages like assembly language to make them compact and efficient. They are stored in a specific location on the boot device, which is usually the first sector of the hard disk or a separate boot partition.

Bootloaders also allow users to choose which operating system they want to boot into in a multi-boot system. For example, a user may have multiple operating systems installed on a computer, and the bootloader will present a menu at startup to let the user select which operating system they want to run.