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Table of contents
Booting in Operating System
Sequencing of Booting
Types of Booting
Booting Process in Operating System
What exactly is dual Booting?
Frequently Asked Questions
Why is Booting required?
What is the main of the Booting in the operating system?
What are the two types of Booting?
How does your system boot up?
Which part of the boot startup is common to all operating systems?
Last Updated: Mar 27, 2024

Booting in Operating System

Author Komal Shaw
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Operating Systems


When we start up a computer we generally refer to it as we are booting it up. It just means that we are loading all the required programs and drivers that are necessary for a computer system to get up and running into the memory. When a computer system boots up, a small set of instructions in the ROM are executed, which set up the system hardware by evaluating it and loading the operating system, allowing it to perform additional tasks. This process is called Booting.

Also see, Types of Operating Systems, Multiprogramming vs Multitasking

Booting in Operating System

The process of starting a computer is known as Booting. It can be triggered by either hardware, such as a button press, or software. A CPU has no software in its main memory when it is turned on; thus, some programs must load software into memory before running. This can be accomplished by the CPU's hardware or firmware or by a separate processor in the computer system.

Restarting a computer is also known as rebooting, and it can be "hard" or "soft," depending on whether the power to the CPU is switched from off to on. A soft boot may optionally clear RAM to zero on some computers. Hardware, such as a button press or a software command, can start hard and soft Booting. When the operative runtime system, often the operating system and some programs, is reached, Booting is complete.

Returning a computer from sleep does not need Booting, but restoring it from hibernation does. At the very least, some embedded systems do not require a visible boot sequence to start running and, when powered on, may run operational programs stored in ROM. All computer systems are state machines, and a reboot may be the only way to get from an unwanted, locked state to a designated zero-state.

A storage dump application can also be loaded during the boot process to diagnose faults with an operating system.

You can also read about the Multilevel Feedback Queue Scheduling and Open Source Operating System.

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Sequencing of Booting


Sequencing of Bootin


When a computer is turned on, the boot procedure begins, launching the operating system. A boot sequence is the first series of operations performed by a computer when turned on. A boot sequence exists on every machine.


1. Boot Loader: Only code stored in the system's memory can be executed by computers powered by the central processor unit. Nonvolatile memories store modern operating systems, application program code, and data. When a computer is turned on for the first time, it must rely solely on the code and data stored in the system's nonvolatile memory. At boot time, the operating system is not fully loaded, and the computer's hardware is incapable of performing many complicated system tasks.

The boot loader, also known as the Bootstrap loader, is the program that initiates the chain reaction that results in the whole operating system being loaded. The boot loader's sole purpose is to load additional software to begin the operating system.

2. Boot Devices: The boot device is where the operating system is loaded from. A modern BIOS (Basic Input/Output System) allows you to boot from a variety of sources. The local hard disc drive, optical drive, floppy drive, network interface card, and USB device are all examples. A boot order can be configured in the BIOS. If you have the boot order set to:

  • Hard Disk Drive 
  • Network 
  • CD Drive

The BIOS will first attempt to boot from the CD drive, and if that fails, it will next attempt to boot from the hard disc drive, and if that fails, it will attempt to boot from the network, and if that fails, it will not boot at all.

3. Boot Sequence: All personal computers follow a common boot sequence. First, the CPU executes a BIOS instruction in memory. A jump instruction in that instruction passes control to the BIOS startup program. This application performs a power-on self-test (POST) to ensure that the computer's devices are operational. The BIOS then runs through the configured boot sequence until a bootable device is found. BIOS loads the boot sector and transfers execution to the boot sector after it has located a bootable device. It will be a master boot record if the boot device is a hard drive (MBR).

The MBR code looks for an active partition in the partition table. If one is identified, the MBR code loads and executes the boot sector of that partition. The boot sector is frequently operating system specific. However, in most operating systems, its primary job is to load and execute the operating system kernel, which allows the operating system to continue booting. Assume there is no active partition or the boot sector of the active partition is faulty. The MBR may then load a secondary boot loader, which will select a partition and load its boot sector, which normally loads the operating system kernel.

Must Read, Components of Operating System

Types of Booting

There are two types of booting in an operating system.

1. Cold Booting: When a computer begins for the first time or when it is in a shutdown state, and the power button is pressed to restart the system, this is known as cold Booting. During cold Booting, the system reads all of the instructions from the ROM (BIOS), and the Operating System is loaded into the system automatically. This type of Booting takes longer than Hot or Warm Booting.

2. Warm Booting: The warm or hot booting process occurs when computer systems reach a state of no response or hang, and the system is then permitted to restart while on. Rebooting is another term for it. There are several causes for this condition, and the only way to fix it is to restart the computer. When we install new software or hardware, we may need to reboot. The system requires a reboot to set software or hardware configuration changes, or sometimes systems may perform improperly or may not respond appropriately. The system must be forced to restart in this instance. To reboot the computer, press the Ctrl+Alt+Del key combination. Otherwise, some systems may have an external reset button that can be used to reboot the machine.

Must Read Multiprocessing Operating System

Booting Process in Operating System

Booting Process in Operating System

When we turn on our computer, it can be started by hardware, such as pressing a button, or by software commands. Because the CPU's main memory contains no software, some processes must load software into the main memory before it can be executed. 

The six steps to defining the operating system's boot procedure are as follows:


Step 1: When the computer system is powered on, BIOS (Basic Input/Output System) runs a series of activities or functionality tests on programs stored in ROM known as POST (Power-on Self Test), which verifies whether the system's peripherals are working properly.

Step 2: After the BIOS has completed the pre-boot activities or functionality test, it reads the bootable sequence from the CMOS (Common Metal Oxide Semiconductor) and searches for the master boot record in the first physical sector of the bootable disc according to the CMOS boot device sequence. If the boot device sequence is as follows:

  • Floppy Disk
  • Hard Disk


Step 3: The master boot record will then search a floppy disc drive for the first time. If the master boot record is not discovered, the hard disc drive will look for it. The CDROM drive will search if the master boot record is not even available on the hard disc. If none of these sources can read the master boot record, ROM displays "No Boot device found," and the system is suspended. The operating system loader, also known as the Bootstrap loader, is loaded from the boot sector of a bootable disc drive into memory when the master boot record is found. A bootstrap loader is specific software that lives in a bootable drive's boot sector.

Step 4: The IO.SYS file is loaded first by the bootstrap loader. The MSDOS.SYS file, which is the DOS operating system's core file, is then loaded.

Step 5: After that, the MSDOS.SYS file looks for Command Interpreter in the CONFIG.SYS file and loads it into memory. The COMMAND.COM file is loaded as the default Command Interpreter of the DOS operating system if no Command Interpreter is specified in the CONFIG.SYS file.

Step 6: The AUTOEXEC.BAT file, which contains a series of DOS commands, must be loaded and executed last. After that, the prompt appears. On the computer system, we can see the drive letter of a bootable drive, indicating that the operating system was successfully installed from that drive.

Must Read Process Management in OS

What exactly is dual Booting?


Dual-booting refers to the installation of two operating systems on a computer system. On such a machine, many operating systems can be installed. A boot loader that knows several file systems and operating systems can occupy the boot space to determine which operating system to boot.

It can boot one of the operating systems on the disc once it has been loaded. There can be several partitions on the disc, each containing a separate operating system. A boot manager program presents a menu when a computer system starts up, allowing the user to select the operating system to use.

You can also read about the Multilevel Queue Scheduling.

Read about Batch Operating System here.

Must Read - Memory hierarchy in computer network

Frequently Asked Questions

Why is Booting required?

The boot device loads the operating system into the main memory.

What is the main of the Booting in the operating system?

Booting is a startup sequence that starts the operating system of a computer when it is turned on. 

What are the two types of Booting?

Cold Booting and Warm Booting

How does your system boot up?

Booting the system is done by loading the kernel into the main memory and starting its execution. 

Which part of the boot startup is common to all operating systems?




In this article, we have extensively discussed Booting in an operating system along with its types and what actually happens when a system is booted up.

We hope that this blog has helped you enhance your knowledge regarding Booting in an operating system.

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