Booting and Dual Booting of Operating System

When a computer or any other computing device is in the powerless state, its operating system remains stored in the secondary storage like Hard Disk or SSD. But, when the computer is started, the operating system must be present in the main memory or RAM of the system.

When a computer system is started, there is a mechanism in the system which loads the operating system from the secondary storage into the main memory or RAM of the system. This is called Booting process of the system.

There are two main scenarios depending on the number of operating systems installed on the machine/computer:

• Single Boot One operating system installed

• Dual Boot Multiple operating systems installed

Let us understand these two concepts in the context of computer booting.

What is Booting of Operating System?

The process of starting a computer or a computing device is called booting. Technically, Booting is a procedure of starting a computer or computer embedded device by loading its operating system from disk into RAM. In other words, Booting is a process of starting a computer system by loading the kernel.

As we mentioned earlier, when computer is switched off, its operating system is stored in the disk. Therefore, on the starting of the computer system, the operating system has to be loaded into the main memory. For this a special computer program is required which locates and loads the operating system into RAM. This special program is called Bootstrap Loader. It is stored in the ROM (Read Only Memory) of the system.

Boot Process Flow

Boot Order Configuration

In modern computer systems, booting can be executed from various devices. The BIOS (Basic Input Output System) of the computer allows users to configure a specific boot order. For example, if there are three devices in the system namely, HDD, CD Drive, and USB Drive, and the boot order is set as follows:

• HDD (Hard Disk Drive)

• CD Drive

• USB Drive

Then the system BIOS will try to boot from HDD first, and if the booting from HDD fails, then it will try to boot from the CD drive, and if it fails to boot, then finally it will try to boot from the USB Drive. If all devices fail to boot, then the system would not boot at all.

What is Dual Booting in Operating System?

When a single computer system has two or more operating systems installed on it, then its booting is called dual booting or multi-booting. Such computer systems can have multiple operating systems installed on them. But in such cases, a question arises that how does the system determine which operating system to boot?

Such systems have a bootstrap loader (like GRUB or Windows Boot Manager) that can understand multiple file systems, and can have multiple operating systems in the boot space. The disk has multiple partitions, thus different operating systems can be stored in different partitions.

Dual Boot Menu Example

When the computer system is started, a menu list is displayed on the screen by a boot manager program that allows the user to select one operating system to run. The selected OS is then loaded into memory and starts execution.

Key Differences

Conclusion

Booting is the fundamental process of loading an operating system from storage into RAM when a computer starts. Dual booting extends this concept by allowing multiple operating systems on one machine, giving users flexibility to choose their preferred OS at startup through a boot manager interface.