bootloader

thumb|GNU GRUB, a popular free-software bootloader thumb|right|Windows Boot Manager thumb|rEFInd, a popular boot manager for EFI and [[UEFI systems]] A bootloader, also spelled as boot loader or called bootstrap loader, is a computer program that is responsible for booting a computer and booting an operating system. If it also provides an interactive menu with multiple boot choices then it is often called a boot manager.

When a computer is turned off, its softwareincluding operating systems, application code, and dataremains stored on non-volatile memory. When the computer is powered on, it typically does not have an operating system or its loader in random-access memory (RAM). The computer first executes a relatively small program stored in the boot ROM, which is read-only memory (ROM, and later EEPROM, NOR flash) along with some needed data, to initialize hardware devices such as CPU, motherboard, memory, storage and other I/O devices, to access the nonvolatile device (usually a block device, e.g., NAND flash) or devices from which the operating system programs and data can be loaded into RAM.