An ISO image includes all the data of files contained on the archived CD, DVD or Blu-ray Disc (BD), or any other disc format. They are stored in an uncompressed format. Any CD or DVD can be archived by .ISO format. It is a true digital copy of the original. The ISO image file is not stored in a container file. These properties make it an attractive alternative to physical media for the distribution of software as it is simple to transfer over the Internet or via a LAN connection.
What is known as a “valid” ISO image is an uncompressed collection of various files merged into one single resulting file, according to definite and standard formatting.
ISO images are not able to store and recreate CD-Audio discs, due to the fact that CD-Audio discs do not use a computer file system. CD-Audio discs are formatted in tracks, and the track numbers, index points and CD time code are encoded into the lead-in of the CD-Audio disc, and these reference points are found throughout the CD-Audio sub-channel. To store an accurate copy of a CD-Audio disc, a different image format must be used, such as DDP or BIN/CUE.
ISO images are also unable to store multi-track disc images.
As of February of 2011, moreover, no “portable” programs for the Windows OS were known to exist that were capable of mounting ISOs on a USB flash (“thumb”) drive or of reading them from such a drive. It is believed[who?] that this was because mounting and/or reading ISOs in Windows NT and later, network-based, versions of Windows OS required a driver, which is inaccessible to users of these operating systems who lack administrative privileges.
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