An ISO archive is what’s called a disc backup - an exact copy of a CD or a DVD disc. ISO files are typically created as CD/DVD backups, but they can also be made “from scratch” using a specialized editor like WinISO. An ISO image can only store a single track of data, so it doesn’t work for music CDs and a few more arcane CD/DVD types.
It may help to think of the .iso image like a kind of archive because it usually contains a number of files and folders. However, unlike other archives (e.g. ZIP or RAR), the ISO archive stores everything in uncompressed form. Some commercial disc archive formats like UIF files and .daa format also support file compression.
To extract an ISO archive you will need to install one of the many ISO image tools. There’s a multitude of applications that can open the ISO format, but most of them are either very expensive or simply lack any defining traits that would let you make an informed choice. So which one should you pick? Depending on your goal, there are two applications that I would recommend.
First, if you only need to open the image, use 7-zip. It’s a free open-source archiver that can open ISO DVD images. It will let you access the contents of the disc archive, but that’s it - 7-zip can’t record, mount or make new .iso archives. It’s a neat and simple tool and it supports Windows and Unix-based computers.
In case you need a bit more functionality you will probably want to install a fully-fetured ISO file software like PowerISO. Yes, it costs money, but the application will let you do almost anything with an ISO or .uif files - extract it, modify, mount it in a virtual drive, convert to a different format, and burn to a real disc. PowerISO only works on Windows, though.
To summarize, ISO is a popular, open disc archive format that is supported by most DVD applications. Some general-purpose archivers can also extract .iso images, but they generally can’t do anything else with them.
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