What is ISO (image) file in Operating System ?

ISO File

An ISO image is an archive file of an optical disc, a type of disk image composed of the data contents from every written sector on an optical disc, including the optical disc file system. ISO image files usually have a file extension of ".iso" .

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

ISO image files 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 - the ISO file.

Burning ISO files to a CD/DVD

One way to make use of ISO files is to burn the file to a physical CD or DVD disc using a process that extracts all the individual folders and files out of the ISO file and places them on the physical media. Windows 7 comes with the built-in Windows Disc Image Burner (not in earlier versions of Windows). Place a blank CD or DVD in your optical drive and double-click the ISO file. Once the disc is burnt, you can use the files and folders the usual way.

Many PCs also come with third-party software for burning discs. If one of these opens when you double-click an ISO file, choose “Burn disc image” or similar command.

There are also free programs for burning CDs or DVDs. Gizmo’s top pick is ImgBurn. Go to Best Free CD-DVD Burning Software for more information.

ISOs are a type of archive

The easiest way to think of an ISO file is more like a .zip or .cab archive file, only without the compression.

An ISO file contains the image of a disk. That means it contains all the files and folders that were on that disk, much like a .zip or .cab file contains a collection of files and folders. The real difference is that an ISO is a byte-for-byte copy of the low-level data actually stored on a disk.

There’s nothing about the ISO format that actually knows about files, folders, or formats. It’s just the raw data from the disk. If interpreted correctly, that raw data may naturally represent files, folders, and formatting details. But, like a disk, the operating system has to look, see what format was used (things like FAT32, NTFS, and the like), and then interpret the contents of the ISO file as if it were reading the raw data from an actual disk.

There are a few ways to deal with ISO files.

Making ISO files

Creating ISO files of CDs or other disks that you own is a convenient way to backup, archive, or (if legal) share them. And it’s actually quite easy to do. There are two approaches:

Create an ISO file from an actual disk. Most CD/DVD burning software includes the ability to “rip” or create an ISO image from a CD or DVD disc. In particular, ImgBurn is perhaps one of the easiest tools to use for this purpose. Just insert your CD, tell ImgBurn where to place and what to name the ISO file, and push a button.

Create an ISO file from a collection of files. ImgBurn can also be used to create an ISO image from files you specify, much as if you were actually burning files to CD or DVD. After collecting the files that you want to place in the image, you can instruct ImgBurn to create an ISO file instead of actually burning to disk.

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.