Image Files - What's the Difference Between .iso and .nrg

[SCDVD]

Does anyone know the difference between an .iso and a Nero .nrg image file? You can select either one in Nero. Are they interchangeable?

[redwudz]

I found this at CDfreaks: http://club.cdfreaks.com/showthread.php?t=142994

Re: .nrg vs .iso

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There is a subtle difference between the .nrg format and the .iso format.
ISO9660 images, as the name already hints, are limited to storing a file-system in ISO9660 format. Thus, this file format cannot be used to store audio content or even TOC information, only the file-system of a single track on a CD/DVD can be represented.
In contrast to that the .nrg format is generic enough to be able to represent *any* disc layout Nero can produce, e.g. mixed mode discs, CD-Audio, CD-Extra, everything Nero can produce either by mastering or by CD/DVD-Copy.

If all you're writing is a ISO9660 filesystem, the .NRG image created in *Track at Once* mode can be mounted just like an ISO9660 filesystem image file (.iso).
Images created in Disc-At-Once mode have a slightly more complicated layout that will need you to specify an offset from which to read the ISO9660 file-system as it has other information prepended. I'm not sure whether this offset is constant so the safest way is to resort to creating TAO images.

[edsmith77]

SCDVD,
If not mistaken, ISO stands for International Standards Organization. This group makes standards for all sorts of stuff. The main reason for the standard is compatibility across systems, machines and countries. However, for this compatibility you do have to pay a price. In this case, is it efficiency. However, if the users adopt the standard then it is very portable.
Now comes Nero. In their infinite wisdom, they have deciced to create their own proprietary format mainly to increase efficiency. So they have modified the ISO standard into a more efficient format but at this time basically only Nero programs can read that format.
On the other hand of course Nero can read ISO standard formats.

Now if "everyone" adopted the Nero format then maybe .....

[Legendsk]

Actually while ISO sounds like it should be an acronym for International Standards Organization - it is not. The actual definition is:
http://www.iso.org/iso/en/aboutiso/introduction/index.html#two
What ISO's name means

Because "International Organization for Standardization" would have different abbreviations in different languages ("IOS" in English, "OIN" in French for Organisation internationale de normalisation), it was decided at the outset to use a word derived from the Greek isos, meaning "equal". Therefore, whatever the country, whatever the language, the short form of the organization's name is always ISO.