What is a ISO file?
ISO — disk image
What is it?
An ISO file is an exact copy of an optical disc: sector by sector, structure included. It isn't an archive of files—it's a snapshot of an entire storage medium.
That's why it can be "mounted"—the system makes it appear as a drive, as though the disc were physically inserted—and why it can be bootable, capable of starting up a computer.
History & origin
The format takes its name from the ISO 9660 standard, which in 1988 defined the file system used on CD-ROMs.
It has outlived the disc drives themselves: today, an ISO is mainly used to distribute an operating system and to create a bootable USB installer.
Why it is useful
A faithful, complete, bootable copy that preserves the exact structure of the original medium.
It's the standard format for distributing operating systems.
Limits & drawbacks
No compression: an ISO is the size of the disc it copies, empty space included in some cases.
It isn't designed to carry just a handful of files—it's overkill for such a simple task.
Practical tips
If you only want to retrieve the contents of an ISO, convert it to ZIP: you'll get the files without the disk structure.
Keep the ISO as it is if you need to create an installation drive: converting it would strip away its bootable nature.
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