Booting Explained: How Computers Start and Load Operating Systems

Understanding the Booting Process

When a computer rests, its OS is stored in a secondary storage such as an SSD or hard disk. When the computer is started, the operating system must be located in the main memory or RAM to start up all the functions. The process of loading the system from a secondary storage into the main memory or RAM is called the booting process.

Different Types of Booting

There are two main types of booting depending on the number of operating systems installed on a machine or computer.

1. Cold (Hard) Boot

A cold boot happens when a computer is turned on from a fully powered-off state. The system undergoes a complete power-on self-test (POST) that “launches” the hardware and loads operating systems from storage to RAM.

2. Warm (Soft) Boot

Warm or soft boot, which is also called a restart, is a process of rebooting a computer without shutting it down completely. Warm boot can be activated with a key combination or a restart command in the OS.

Warm boot skips certain hardware initialization processes; however, it is also a valuable booting option in some scenarios.

Power-On Self-Test (POST)

Power-On-Self-Test booting is an integral part of a booting cycle, which consists of a diagnostic routine for hardware components. It tests the status of hardware components such as CPU, memory, storage, and others.

It’s basically a screening aimed at finding problems that may prevent booting. If an issue is found, POST usually displays an error message. If the process was seamless, then the computer just loads an operating system.

The Role of the Master Boot Record (MBR)

Master Boot Record (MBR) is a boot loader that BIOS or UEFI looks for, after POST is complete.

Usually, the boot loader is located in the first layer of the hard drive. It consists of two main components: bootloader code, which identifies where the OS is stored, and a partition table, which defines different parts of the disk.

Once the bootloader is executed, it loads the OS kernel into memory, and the system takes over.

Steps Involved in the Booting Process

The booting process includes the following steps:

1. Receiving the power supply to the motherboard and other components.

2. Running the BIOS or UEFI firmware.

3. Firmware identifying bootable devices.

4. POST execution and testing of hardware.

5. Activating the bootloader.

6. Loading the OS kernel.

7. Kernel is starting background services and interfaces.

8. Completion of the boot cycle.

What Does Dual Booting Mean?

When there are two OS on the machine, then the concept of dual booting is applicable. A user can usually choose which operating system to load before starting the process.

When the system starts, it usually gives a menu with options of which OS to load.

Dual booting is often used by developers, IT professionals, and users who need access to multiple environments.

Comparing Booting and Dual Booting