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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?

Ben
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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. – Daniel R Hicks Apr 22 '13 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 '13 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 '13 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 '13 at 13:08
  • Just as a trivia, `iso` is also Greek for "same" (or so I've heard) – CamelBlues Apr 22 '13 at 16:06
  • Wanted to point out that some programs used different extensions such as CDR or IMG. But ISO seemed to become the standard eventually. – Zan Lynx Apr 22 '13 at 16:29
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    @ZanLynx note that some CD images are *not* uncompressed bitwise-copies of an ISO-9660 or ISO-13346 file system; those *should not* use an .ISO extension. In your examples, CDR is just the MacOS name for ISO, but IMG could literally be anything (including a floppy disk image). – KutuluMike Apr 22 '13 at 17:36
  • what a question! :) – ruben Apr 22 '13 at 21:03
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    This has really been bugging me: It's not a .ISO it's **an** .ISO! Right? – AnnanFay Apr 22 '13 at 21:42
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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 '13 at 22:20

4 Answers4

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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.

user215113
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Simon
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From the ISO 9660 standard.

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

Brad Patton
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Mathieu Westphal
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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.

mpy
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    So why isn't the filetype `.iofs` or `.ios`? – Izkata Apr 22 '13 at 13:55
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    @Izkata because the short name of the organization is ISO http://www.iso.org/iso/about/about#2012_aboutiso_iso_name-text-Anchor – Evan Harper Apr 22 '13 at 14:02
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    `.iofs` is ruled out at once due to DOS's `8.3` convention (also pointed out by @aldric), for the latterhave a look at http://en.wikipedia.org/wiki/International_Organization_for_Standardization why ISO isn't abbreviated as IOS. – mpy Apr 22 '13 at 14:03
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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"? – Keith Thompson Apr 23 '13 at 00:16
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    He probably meant [this wikipedia article](http://en.wikipedia.org/wiki/ISO_image). – jao Apr 23 '13 at 07:24