These instructions typically start an input operation from some peripheral device (which may be switch-selectable by the operator). Some earlier computer systems, upon receiving a boot signal from a human operator or a peripheral device, may load a very small number of fixed instructions into memory at a specific location, initialize at least one CPU, and then point the CPU to the instructions and start their execution.

The computer first executes a relatively small program stored in read-only memory (ROM, and later EEPROM, NOR flash) along with some needed data, to initialize RAM (especially on x86 systems), to access the nonvolatile device (usually block device, eg NAND flash) or devices from which the operating system programs and data can be loaded into RAM. When the computer is powered on, it typically does not have an operating system or its loader in random-access memory (RAM). When a computer is turned off, its software‍-‌including operating systems, application code, and data‍-‌remains stored on non-volatile memory. A bootloader, also spelled as boot loader or called boot manager and bootstrap loader, is a computer program that is responsible for booting a computer.

Boot manager pc