What is an ISO File?

ISO Image Definition & How To Burn, Extract, and Create Image Files

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An ISO file, often called an ISO image, is a single file that's a perfect representation of an entire CD, DVD, or BD. The entire contents of a disc can be precisely duplicated in a single ISO file.

Think of an ISO file like a box that holds all the parts to something that needs built - like a child's toy you might buy that requires assembly. The box that the toy pieces come in does you no good as an actual toy but the contents inside of it, once taken out and put together, become what you're actually wanting to use.

An ISO file works in much the same way. The file itself is no good unless it can be opened, assembled, and used.

Where You'll See ISO Files Used

All ISO images end in the file extension ISO, and are often used to distribute large programs over the Internet due to the fact that all of the program's files can be neatly contained as a single file.

One example can be seen in the free Ophcrack password recovery tool (which contains an entire operating system and several pieces of software). Everything that makes up the program is wrapped up in one file. The file name for the most recent version of Ophcrack looks like this: ophcrack-vista-livecd-3.6.0.iso.

Ophrack certainly isn't the only program to use an ISO file - many types of programs are distributed this way. For example, most bootable antivirus programs use ISO, like the bitdefender-rescue-cd.iso ISO file used by Bitdefender Rescue CD.

In all those examples, and the thousands of others out there, every single file required for whatever tool to run is included in the single ISO image.

Like I mentioned already, that makes the tool really easy to download, but it also makes it super easy to burn to a disc or other device.

Even Windows 10, and previously Windows 8 and Windows 7, can be purchased directly by Microsoft in the ISO format, ready to be extracted to a device or mounted in a virtual machine.

How to Burn ISO Files

The most common way to make use of an ISO file is to burn it to a CD, DVD, or BD disc. This is a different process than burning music or document files to a disc because your CD/DVD/BD burning software must "assemble" the contents of the ISO file onto the disc.

Windows 10, 8, and 7 can all burn ISO images to a disc without using any third-party software - just double-tap or double-click the ISO file and then follow the wizard that appears.

The same logic applies when burning an ISO file to a USB device, something that's much more common now that optical drives are becoming much less common.

Burning an ISO image isn't just an option for some programs, it's required. For example, many hard drive diagnostic tools are only usable outside the operating system. This means that you'll have to burn the ISO to some form of removable media (like a disc or a flash drive) that your computer can boot from.

While less common, some programs are distributed in ISO format but aren't designed to be booted from. For example, Microsoft Office is often made available as an ISO file and is designed to be burned or mounted, but since it doesn't need to be run from outside of Windows, there's no need to boot from it (it wouldn't do anything if you tried).

How to Extract ISO Files

If you don't want to actually burn an ISO file to a disc or USB storage device, most compression/decompression software programs, like the free 7-Zip and PeaZip programs, will extract the contents of an ISO file to a folder.

Extracting an ISO file copies all of the files from the image directly into a folder that you can browse through like any folder you'd find on your computer. Although the newly created folder can't be directly burned to a device like I discussed in the section above, knowing that this is possible might come in handy.

For example, let's say you've downloaded Microsoft Office as an ISO file.

Instead of burning the ISO image to a disc, you could extract the installation files from the ISO and then install the program like you normally would any other program.

Every unzip program requires a different set of steps, but here's how you can extract an ISO image using 7-Zip: Right-click the file, choose 7-Zip, and then select the Extract To "<folder name>\" option.

How to Create ISO Files

Several programs, many of them free, let you create your own ISO file from a disc or a collection of files you've chosen.

The most common reason to build an ISO image is if you're interested in backing up a software installation disc or even a DVD or Blu-ray movie.

See How To Create an ISO Image File From a CD, DVD, or BD for help doing that.

How to Mount ISO Files

Mounting an ISO file that you've created or downloaded from the Internet is sort of like tricking your computer into thinking that the ISO file is a real disc. This way, you can "use" an ISO file just like it was on a real CD or DVD, only you didn't have to waste a disc, or your time burning one.

One common situation where mounting an ISO file is helpful is when you're playing a video game that requires the original disc be inserted. Instead of actually sticking the disc in your optical drive, you can just mount the ISO image of that game disc that you previously created.

Mounting an ISO file is usually as simple as opening the file with something called a "disc emulator" and then choosing a drive letter that the ISO file should represent. Even those this drive letter is a virtual drive, Windows sees it as a real one, and you can use it as such too.

One of my favorite free programs for mounting ISO images is WinCDEmu because of how easy it is to use (plus it comes in this portable version). Another one I feel good recommending is Pismo File Mount Audit Package.

If you're using Windows 10 or Windows 8, you're lucky enough to have ISO mounting built in to your operating system! Just tap-and-hold or right-click the ISO file and choose Mount. Windows will create a virtual drive for you automatically - no extra software required.

Note: Although mounting an ISO file is very useful in some situations, please know that the virtual drive will be unreachable anytime the operating system isn't running. This means it's entirely pointless to mount an ISO file that you want to use outside of Windows (like what's required with some hard drive diagnostic tools and memory testing programs).