A .ISO is a digital copy of a cd or dvd. Almost 90% of all digital copys end on ".ISO". Why is this? Was there someone that called it .ISO and everyone just copied it?

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    Note that there are thousands of ISO standards, in diverse categories. You'll often here, eg, of "ISO-9000", a standard for running a business. There are standards for paper, for paint, for railway engineering, etc. Apr 22, 2013 at 11:17
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    Soon there will be an ISO standard for how to ask and answer questions about the ISO standards. Better get ready! ;-)
    – Warren P
    Apr 22, 2013 at 11:38
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    And the three letter extension (.ISO) was used due to that being the standard for DOS/Windows systems many of which could not handle longer filenames or extensions.
    – adric
    Apr 22, 2013 at 11:44
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    Great question, considering how large the ISO standards body is, and how many standards they have, why did a CD format get named after it?
    – MarcusJ
    Apr 22, 2013 at 13:08
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    It's "an ISO", but "a dot-ISO". Whether the phrase begins with a vowel depends entirely on whether you pronounce the dot at the beginning. :p
    – neminem
    Apr 22, 2013 at 22:20

4 Answers 4


From the ISO 9660 standard.

But it's just a way to know what a file is about.

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    Thanks its all clear now! It was me failing for not searching it up on Wikipedia.
    – Ben
    Apr 22, 2013 at 10:04
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    The people that coined this term must admit that it does not contain much information. ".966" would have been much more meaningful. Apr 23, 2013 at 21:37

The origin is the ISO 9660 file system which is used on CD-ROM. The extension .iso remained also for DVDs and Blu-Rays which use the UDF (ISO/IEC 13346) file system. See here for details.

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    +1 for mentioning that it does not necessarily contain an image with the ISO 9660 file system. Apr 22, 2013 at 12:38

The name is derivated from a norm issued by the International Organization for Standardization which specifies the file system on an optical medium [1]. That norm has the abbreviation ISO 9660 [2] and you can guess now why a CD-ROM image (and later on a DVD-ROM image) usually is named .iso.

[1] http://en.wikipedia.org/wiki/ISO_9660

[2] Some confusion can arise why ISO isn't an acronym of International Organization for Standardization. Quoting once again Wikipedia:

Recognizing that its initials would be different in different languages, the organization adopted ISO, based on the Greek word isos (ἴσος, meaning equal), as the universal short form of its name.


The .iso extension is an alternate or a shortened form of .iso9660 or .isoimg, which could stand for "ISO 9660-compliant disk image."

The original ISO 9660 standard appears to have been produced in 1988, when PCs were still using 8.3-character filenames (e.g. names could be only 8 characters long, and extensions only 3), so ISO was likely the first choice for shortening the extension to three characters.

Source: Wikipedia (.isoimg) and Wikipedia (.iso9660)

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    I've never seen a file with a .isoimg extension, even on systems that support arbitrarily long extensions, the Wikipedia article you link to doesn't mention it, and a Google search doesn't show anything. Do you have a basis for .iso being short for .isoimg, as opposed to, say, the phrase "ISO image"? Apr 23, 2013 at 0:16
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    He probably meant this wikipedia article.
    – jao
    Apr 23, 2013 at 7:24

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