Booting

Execution

• A CPU loads the next instruction from memory
• This instruction is executed
• This process repeats

Where does the first instruction come from?

Volatility

• Most operating systems are stored in non-volatile memory
• CPUs in most computers execute instructions from volatile memory
• A set of operations is needed to move the operating system to a location that is executable

First-stage boot loader

• Most modern systems include multiple stages of booting
• The first step typically involves loading and executing firmware from a dedicated storage device
• Examples include BIOS and UEFI

Second-stage boot loader

• The initial boot loader is usually tightly coupled to the device
• It is basic and has limited size
• It is used to load a more complete bootloader that loads the full OS
• Examples include GRUB, Syslinux, NTLDR, and BOOTMGR

GRUB

• Popular boot loader used with Linux systems
• Supports multiple operating systems