The extension .ISO refers to files of the type, ISO disk images. These are the exact copies of data present on a CD or DVD. The file is also capable of storing the exact structure of file system information.

These ISO files are usually used for backup purposes to store the data present on vital DVD and CD resources. One particular case where ISO files are used is also seen where the PCs don't have a physical CD or DVD drive present to read the disk data. Hence a Soft-copy version such as the ISO copy of the disk is used in such cases.