A bootloader is a program that loads and launches a program or an operating system from boot.
A bootloader is a small program that have the full functionality of an operating system, but is specially constructed to be able to load another program to allow the initiation of the operating system. Often, multi-stage boot loaders are used in this case several small programs complement each other in sequence, until the last of them loads the operating system.
A hypothetical machine language for the system of initiation, could be as simple as the following eight instructions, that read the data from the tape:
1. Please register P = 8
2. Make sure the paper tape is positioned
3. If not return to step 1
4. A byte read from the tape
5. If you reached the end of the tape skip to step 8
6. Store the data read from the register address P
7. increment the P register
8. jump to a
In modern computers the boot process begins with the execution by the CPU of a program contained in ROM (IBM PC's BIOS) in a predefined address (the CPU is programmed to run this program automatically after a reset). This program contains rudimentary functionality to search for devices that may contain an operating system and are therefore likely to participate in a boot.
