Browse Definitions :

disk image

What is a disk image?

A disk image is a compressed file that contains a copy of the entire contents of a computer's hard drive or other storage media, such as optical discs or solid-state drives. The disk image represents the content exactly as it is on the original storage device, including both data and structure information.

A disk image is a byte-by-byte, sector-by-sector copy of the content on the original source drive. These images provide a single reference of a machine configured for an organization's computing environment.

Photo of various types of storage media, including a hard drive, compact discs and a USB flash drive.
Disk images are made of the contents of various types of computer storage media.

How does a disk image work?

A disk image includes files and file folders, boot files, directories, file allocation tables, operating system (OS) attributes, slack space and unused storage capacity. Disk imaging software is used to make an image of a completely configured system. Because of its large size, a disk image file is compressed and stored on a secondary storage device or in cloud storage. Hard drive disk images can be saved as a virtual hard disk.

A disk image provides a single, consistent source for all computers in a group or organization on which the information on it is installed. It also can be mounted so that users can view it on their desktop as though it were an external drive. Authorized users have access to all file folders within a mounted disk image.

For enhanced security, the contents of a disk file can be encrypted and password-protected, much like any other computer system drive or device. There are many file formats used for disk images, which are identified by specific three-letter file extensions.

How are disk images used?

Disk images serve a variety of use cases, including the following:

  • Computer forensics.
  • Copying CDs and DVDs.
  • Creating portable versions of a user's system.
  • Data protection.
  • Disaster recovery.
  • Disk cloning or ghost imaging.
  • Distribution of applications and OSes.
  • Large-scale OS deployment and system migration.
  • System backup.

Is a disk image the same thing as an ISO file?

Disk images and International Organization for Standardization (ISO) files are similar but have different origins. The disk image file format extension IMG originated to replicate images on floppy disks. IMG disk image files are still in use, but they are often converted to the ISO format as a way to archive the entire contents of optical media as a single file.

ISO is the generally accepted format for disk images and is recognized by most OSes, which typically include native tools for extracting and reading disk image files in ISO format. ISO files make it easier to distribute software for installation via the internet.

In an uncompressed form, there is no discernible difference between an IMG and ISO disk image file. Compressing a disk image conserves storage, but some devices might not be able to read the image. It's possible to convert IMG files to the ISO format and vice versa using special file-conversion software.

Since it represents the contents of a physical drive, a disk image can be safely deleted after its associated application is successfully installed.

How do disk images get mounted?

In Microsoft Windows, disk images are mounted and unmounted with the File Explorer tool or the Disc Image Tools tab on the Windows ribbon.

For systems running macOS, programs are distributed in the Apple Disk Image format, identified as DMG files. Variants of the open source Linux file system natively support mounting disk images as virtual disks.

Disk image vs. disk clone vs. golden image

A disk image, disk clone and golden image have similarities in that each produces a replica of all the contents on a drive. However, there are some differences:

  • A disk image is a compressed copy of a prepared application environment that allows a granular data restore to occur. Multiple images can be stored per disk and incrementally updated.
  • A disk clone is an uncompressed copy of a drive that can be immediately used in a production environment to replace a failing hard disk drive. Cloning is faster than creating a disk image, but only one clone per disk can be stored, and new data can't be added to a clone.
  • A golden image is a snapshot of a configured disk, server, system or virtual machine that is used to deploy new instances on a network. Master image and clone image are synonymous terms with golden image.

Disk imaging pros and cons

Having an available reference machine image makes it easier for organizations to upgrade their computer environment. All computing devices that have had the disk image installed will have uniform configuration settings and programs, saving time when upgrading computers and peripheral components.

On the other hand, a disk image represents a snapshot of a drive at a given point in time. If new machines are added to the environment after the disk image is made, those newer devices might not receive security patches or software updates, delaying their provisioning for production environments.

Learn what you need to know about snapshots vs. backup.

This was last updated in June 2023

Continue Reading About disk image

  • local area network (LAN)

    A local area network (LAN) is a group of computers and peripheral devices that are connected together within a distinct ...

  • TCP/IP

    TCP/IP stands for Transmission Control Protocol/Internet Protocol and is a suite of communication protocols used to interconnect ...

  • firewall as a service (FWaaS)

    Firewall as a service (FWaaS), also known as a cloud firewall, is a service that provides cloud-based network traffic analysis ...

  • identity management (ID management)

    Identity management (ID management) is the organizational process for ensuring individuals have the appropriate access to ...

  • single sign-on (SSO)

    Single sign-on (SSO) is a session and user authentication service that permits a user to use one set of login credentials -- for ...

  • fraud detection

    Fraud detection is a set of activities undertaken to prevent money or property from being obtained through false pretenses.

  • change management

    Change management is a systematic approach to dealing with the transition or transformation of an organization's goals, processes...

  • IT project management

    IT project management is the process of planning, organizing and delineating responsibility for the completion of an ...

  • chief financial officer (CFO)

    A chief financial officer (CFO) is the corporate title for the person responsible for managing a company's financial operations ...

  • core HR (core human resources)

    Core HR (core human resources) is an umbrella term that refers to the basic tasks and functions of an HR department as it manages...

  • HR service delivery

    HR service delivery is a term used to explain how an organization's human resources department offers services to and interacts ...

  • employee retention

    Employee retention is the organizational goal of keeping productive and talented workers and reducing turnover by fostering a ...

Customer Experience
  • martech (marketing technology)

    Martech (marketing technology) refers to the integration of software tools, platforms, and applications designed to streamline ...

  • transactional marketing

    Transactional marketing is a business strategy that focuses on single, point-of-sale transactions.

  • customer profiling

    Customer profiling is the detailed and systematic process of constructing a clear portrait of a company's ideal customer by ...