What is a bootable ISO? Comparison with normal ISO & other installation methods

Provisioning systems and making them business-ready is one of the most crucial responsibilities of IT teams. Additionally, restoring systems in the event of a breakdown is critical to ensure business continuity.

In such cases, re-installing the operating systems using a CD/DVD can be increasingly complex and costlier since they cannot be reused once the file is burned into them. Also, most modern laptops do not have the provision of an optical disk drive. These reasons have contributed to the growing popularity of USB devices as bootable ISOs.

This article covers the following topics:

What is a bootable ISO?

A bootable ISO is an Image Storage Optical (ISO) file containing the necessary files required to boot a computer to recover or reinstall an OS, using a CD, DVD, or a USB drive. The bootable ISO includes a boot loader, an operating system, and the other required files to allow the computer to boot directly into that environment.

What are the components of a bootable ISO?

A bootable ISO is a structured collection of multiple files and scripts such as system files, configuration scripts, bootloaders, and so on. Here’s a breakdown of the components of a bootable ISO:

• Bootloader - On system startup, this program loads the operating system into the computer's memory. On initiation of the boot process, this program hands over the entire control to the operating system.
• Operating System Files - These files form the core of the bootable ISO and include all the necessary system files, folders, drivers, and libraries required to install or run the operating system.
• Boot Configuration Data (BCD) - This is a platform-independent configuration file that stores information about how the Windows operating system should boot. It defines what to load, how to load it, and where to find the OS kernel and other essential components.
• File System Structure - Bootable ISOs use a standard file system layout so that BIOS or UEFI firmware can understand them. Formats like ISO9660, UDF, or El Torito are commonly used to make sure the ISO is recognized as bootable.
• Setup or Installer Script - This component guides the user through the installation process. It may launch a GUI-based wizard (like Windows Setup) or a terminal-based interface (like Debian Installer).
• Optional Tools and Utilities - Many bootable ISOs come with extra utilities—disk partitioners, system diagnostics, file recovery tools, and even web browsers—especially in rescue ISOs or Linux live environments.

What are the benefits of a bootable ISO?

As stated at the beginning of this article, USB drives have now become popular choices for bootable ISOs. However, let us take a look at the broader benefits of bootable ISOs:

• Bulk Deployment: Admins can install or repair multiple systems using a single image, thus saving the time required to create multiple bootable images as well as using multiple drives.
• Diagnostic Utilities: In case of OS failure, bootable ISOs can be used to launch system repair tools.
• Testing Environments: Bootable ISOs can seamlessly help test new OSes or applications on virtual machines, by setting them up promptly without affecting your main system.

What are the differences between bootable ISO and other installation options?

There are several options to install operating systems such as PXE boot, non-installable CDs, and so on. Here's a detailed understanding of the functionalities of the various installation options, their pros, and cons.

How to create a bootable ISO?

Creating bootable ISOs can be a lifesaver, not just when you are managing multiple systems but also for troubleshooting and backups. This process can be done seamlessly either using the native capabilities offered by the operating systems, i.e. via the terminal or via OS imaging and deployment solutions like OS Deployer.

FAQs on bootable ISO

1) What is the difference between a bootable USB and a normal USB?

A bootable USB is used to install operating systems or troubleshoot systems and contains files such as the bootloader, operating system, and other important files required to ensure that the system boots accordingly.

A normal USB, on the other hand, is just a storage device, like a CD or a DVD. Users can store different types of files like documents, music, or videos in it. A bootable USB cannot have other files other than that required to boot the systems.

2) What is a bootable copy?

A bootable copy is a cloned version of a hard disk or an SSD that can be used to boot the system. In addition, it also contains clones of the contents of the hard disk including the files, folders, installed programs, user accounts, settings, and other data.

3) What is the difference between ISO and EXE files?

An ISO file is a complete image of a drive that stores the OS installers. The ISO file must be mounted on a USB drive or a disk, commonly referred to as burning, to be made usable for OS installation and troubleshooting.

An EXE file is a Windows executable that can run directly in the system on being double-clicked by a user.